Storm-ravaged residents of New York and New Jersey began urgent recovery efforts Tuesday after a nighttime pummeling from Hurricane Sandy, which caused widespread flooding, raging fires and broad power outages and left at least 40 people dead from Connecticut to North Carolina.

The devastating storm’s torrential rains and howling winds left behind floodwaters from Lower Manhattan to Atlantic City, N.J., while firefighters continued to battle a still-smoldering fire that consumed scores of homes in a waterfront neighborhood in Queens.

Mighty New York City was largely paralyzed, its pivotal subway system flooded and numerous bridges and tunnels shut down. Wall Street’s financial markets were shuttered for a second day — the longest weather-related closure in 124 years — while authorities warned that it would be days, if not weeks, before the city returned to normal.

“The damage we suffered across the city is clearly extensive, and it will not be repaired overnight,” Mayor Michael R. Bloomberg (I) said in a morning news conference. He said all New York area airports were still shut down Tuesday and that public transportation in the city “remains closed until further notice.” About 750,000 New Yorkers are without power, the mayor said.

From a raised catwalk in a pier-side Brooklyn warehouse, Dave Shamoun, 58, the owner of a marine industry supplier, surveyed the soggy wreckage standing in about 5 ½ feet of water in his 15,000-square-foot space. A pair of forklifts were inoperable, their electrical innards damaged by saltwater. A box of electrical switches for the Suez Canal had floated halfway across the warehouse.

“This is New York’s Katrina,” Shamoun said, referring to the hurricane that ravaged New Orleans in 2005.

“The level of devastation at the Jersey Shore is unthinkable,” New Jersey Gov. Chris Christie (R) told reporters earlier Tuesday. He said he was about to take a helicopter tour to assess the damage but “there is no place for me to land on the barrier islands.” He said 2.4 million New Jersey households are without power — twice the number that lost electricity during Hurricane Irene — and he estimated that full restoration would take longer than the eight days it took after that storm last year.

“It is beyond anything I thought I’d ever see,” Christie said of the damage to his state. “Terrible.... No question in my mind, the devastation that happened to New Jersey is beyond what happened to anyone else” from Sandy.

President Obama signed federal emergency declarations for 10 states and the District of Columbia, permitting state officials to begin making requests for federal assistance, including manpower and equipment.

The president had canceled campaign plans for Monday and Tuesday so he could remain at the White House and oversee the federal response to the storm. Obama later canceled campaign events scheduled for Wednesday in Ohio, the White House announced.

The federal government announced that its offices in Washington would reopen Wednesday but said employees would have the option to take unscheduled leave or perform unscheduled telework.

Obama held a conference call Tuesday with 13 state governors, seven city mayors and top administration officials to discuss response efforts, the White House said.

Later, after visiting the headquarters of the Red Cross in Washington, Obama told reporters he has instructed federal agencies to be proactive in responding to the disaster. “There’s no excuse for inaction at this point,” he said. “My message to the federal government: No bureaucracy. No red tape.”

Obama said he told the state and local officials, “We are going to do everything we can to get resources to you and make sure that any unmet need that is identified, we are responding to it as quickly as possible.” He added that if the governors and mayors are “getting no for an answer somewhere in the federal government, they can call me personally at the White House.” Obama also urged people to look out for each other, particularly the elderly, and to donate to the Red Cross.

“During the darkness of the storm, I think we also saw what’s brightest in America,” he said, citing images of New York nurses carrying newborns to safety, firefighters battling to save homes and lives in Queens and the Coast Guard rescuing people from a sinking ship off North Carolina.

“This is a tough time for a lot of people,” Obama said. “But America is tougher. And we’re tougher because we pull together. We leave nobody behind. We make sure that we respond as a nation.”

GOP challenger Mitt Romney also shelved many of his campaign plans, but held a “storm relief” event in Dayton, Ohio, that featured the trappings of a political “victory rally.” The campaign also announced that Romney would formally resume full campaigning on Wednesday in Florida.

At the Dayton event, Romney ignored repeated questions from reporters about whether he wished to scale back the Federal Emergency Management Agency, a position he advocated during a GOP primary debate. FEMA is in charge of coordinating the federal response to disasters such as Hurricane Sandy. The Dayton event promptly drew criticism from Ohio Democratic Party Chairman Chris Redfern, who charged that Romney “chose to politicize” the storm damage by holding a campaign-style rally.

Bloomberg and other officials said they expected their jurisdictions to be ready for Election Day next Tuesday, though they did not provide details about what challenges they might face. Christie, who had been floated as a potential GOP presidential candidate and has campaigned on Romney’s behalf, offered praise Tuesday for Obama’s efforts during the storm and scoffed at speculation about Sandy’s potential impact on the election.

“I spoke to the president three times yesterday,” Christie said on CNN. “He’s been incredibly supportive and helpful to our state, and not once did he bring up the election.... If he’s not bringing it up, I’m certainly not going to bring it up.”

As the storm barreled ashore Monday night, it transformed the streets of Atlantic City into rushing rivers and inundated large swaths of Lower Manhattan, plunging much of the city’s storied skyline into darkness. A 13-foot surge of seawater flooded streets, tunnels, parking garages and parts of the electrical system in Lower Manhattan, forming white-capped cascades in the Ground Zero construction zone and inundating the financial district.

On the Rockaway peninsula in Queens, nearly 200 firefighters battled a raging fire that consumed more than 80 houses and prompted a daring rescue of about 25 people from an upstairs apartment. Fire personnel were still battling the blaze on Tuesday morning, though officials said the fire had been contained.

Among those who lost their homes in the blaze was Rep. Robert L. Turner (R-N.Y.). His house in Breezy Point, Queens, was destroyed, but neither he nor his wife was harmed.

“I, along with many other Breezy Point residents, lost our homes last night and I am grateful that my family and I are safe after this destructive storm,” Turner said later in a statement. “I hope you will join me in lending a hand to those who were less fortunate and keep everyone impacted by this storm in your thoughts and prayers.”

The storm claimed at least 10 lives in New York City “and tragically we expect that number to go up,” Bloomberg said.

Overall, the death toll climbed to at least 40, including 17 victims in New York state, the Associated Press reported. Storm-related fatalities were also reported in at least seven other states. Many of the victims were killed by falling trees, AP said.

One of the most gripping dramas of the storm came at New York University’s Tisch Hospital, which evacuated more than 200 patients to other facilities — including 20 infants from neonatal intensive care — after a backup generator failed. Nurses frantically kept patients alive with respirators operating on battery power as they gingerly carried them down darkened stairwells and into the howling gale outside.

Bloomberg said there were no reports of fatalities at any hospitals despite a loss of power at several of them during the storm.

Transit authorities said the storm was the most destructive in the 108-year history of the New York subway system, and they offered no timeline for restoration of service early Tuesday. “We are assessing the extent of the damage and beginning the process of recovery,” Metropolitan Transportation Authority Chairman Joseph J. Lhota said in a statement.

Later, in response to a question at his news conference, Bloomberg said it could take four or five days for the subway system to resume normal operations.

Authorities in New Jersey said rising water overwhelmed a natural berm in Bergen County, prompting frantic efforts to rescue hundreds of stranded residents of the towns of Moonachie, Little Ferrie and Carlstadt. Christie said residents in three trailer parks in Moonachie had to await rescue on roofs.

“We’ve rescued hundreds of folks out of there,” Christie said on CNN. “We’ll have to rescue hundreds more throughout the day.”

Christie also reiterated criticism of the mayor of Atlantic City for not heeding an evacuation order.

In all, more than 8 million people in the East lost power, and more than 1 million in a dozen states were ordered to evacuate.

Three nuclear power reactors were shut down because of electricity issues during the storm, while a fourth plant, Oyster Creek in New Jersey, remains in “alert” mode because of high water levels in its water intake structure, the Nuclear Regulatory Commission said Tuesday.

The three reactors to experience trips, or shutdowns, during the storm were Nine Mile Point 1 in Scriba, N.Y., Indian Point 3 in Buchanan, N.Y.; and Salem Unit 1 in Hancocks Bridge, N.J., the NRC said.

After claiming 69 lives in the Caribbean, Hurricane Sandy was officially reclassified as a nontropical storm because of its unusual dynamics shortly before it came ashore at 8 p.m. Monday in Atlantic City. But it still packed sustained hurricane-force winds of 80 mph or more, and it produced dangerous flood tides as high as 13 feet , the National Hurricane Center said.

By about 4:30 a.m. Tuesday, Sandy was classified a post-tropical cyclone. Meteorologists said Sandy lost some characteristics of a tropical storm because of its collision with arctic air. But that collision also created an unusually large and dangerous storm system spanning nearly 1,000 miles and dumping as much as 2 feet of snow in mountainous areas.

In its latest incarnation, Sandy was weakening while moving slowly westward across southern Pennsylvania, its maximum sustained winds dropping to 45 mph, the National Hurricane Center said. It said high-wind warnings were in effect along the central to southern Appalachians and across portions of the Great Lakes. Storm warnings remained in effect along the Mid-Atlantic and New England coasts from Virginia to Massachusetts and across the Great Lakes.

U.S. stock markets remained closed for a second day Tuesday. It was the first time that the New York Stock Exchange was closed for two straight days because of weather since a major blizzard struck the city in 1888.

The stock exchange announced that it would reopen Wednesday.

Federal government offices were closed for most employees Tuesday, most schools, colleges and universities shut their doors for another day, and Amtrak canceled Northeast service.

From Manhattan’s East Village to Brooklyn’s Red Hook, many New Yorkers were reeling Tuesday in the storm’s aftermath without electricity or running water, largely restricted to their own neighborhoods in the absence of public transportation. Ground-level businesses, apartment dwellers and homeowners pumped out floodwaters and tried to salvage waterlogged possessions.

In his warehouse by Red Hook’s piers, Shamoun, the owner of Technico Marine Corporation, sounded irritated when he noted that a friend had urged him to contact FEMA to help raise the funds needed to get his business back up and running. He said he abandoned an effort last year to secure a loan from FEMA after Hurricane Irene because the paperwork — 30 pages’ worth — was too cumbersome to complete without an “army of secretaries,” and because the agency would not have been able to provide a better loan rate than his own banker.

“I don’t think the government is going to do anything for me,” Shamoun complained. “It’s disheartening.”

In Lower Manhattan, the inconveniences were compounded by the risks of crossing the street. Street lights were out and traffic cops were scarce, leaving pedestrians to play a dangerous game of chicken with cars, cabs and trucks speeding along First Avenue.

In Brooklyn, Elizabeth Freund, 49, returned to her home in Red Hook Tuesday morning to find her bedroom and her daughter’s room in nearly three and a half feet of water. “My bedroom is floating, my office if floating, my daughter’s room is floating,” she said.

Gino Vitale, a Brooklyn landlord who owns 25 apartment buildings in the area, said 16 of them were inundated. But other apartments on lower-lying streets around the block were hit harder, leaving them submerged in more than eight feet of water, he said.

David Borchon, 28, watched the storm from the third floor of his family apartment at the Jacob Riis Housing Projects on the Lower East Side. The waters covered 12th Street, rising to the tops of cars and flooding the Con Edison power station, he said. FDR Highway seemed to merge with the East River, Borchon said.

As the floodwaters rose, the power station exploded, twice, leaving the entire area in darkness.

“We heard it go boom,” Borchon said. “I saw a big green light; it shook the projects.” Now, he said, “we don’t have no water, no electricity. We can’t even flush the toilet. And we’re not going to have water for five days.”

The Hamptons, the ocean-front vacation spot of hedge fund moguls, entertainers and old money, lost power at about 4:30 p.m. on Monday when Sandy’s leading edge grazed Long Island. Many of the communities remained cut off early Tuesday morning by downed oak trees that lay across the privet-lined two-lane roads.

In the bay front village of Sag Harbor the combination of flooding, snapped trees and power lines meant residents would be without power for seven to 10 days, mayor Brian Gilbride said via radio early Tuesday.

In southern Brooklyn, many residents were without power Tuesday as they coped with debris brought in by Sandy’s winds or storm surge.

“It didn’t seem as if anyone had prepared their homes before the storm came in,” said Ned Berke, who edits a news Web site covering the old fishing community of Sheepshead Bay, where some residents had tried to ride out the storm in their wood-frame homes and bungalows. By 5 p.m. Monday, he said, people were palpably nervous and were feebly trying to secure their property and nail boards on windows.

“By the time we realized, ‘shoot, this place is going to flood,’ it was too late,” Berke said. “It was too dangerous to try to go outside.’’

At high tide, ocean water funneled through the bay, ripping apart a 100-year-old esplanade. Sailboats were cut from their moorings, and some sank. Storefronts filled with water and mud. The plate glass windows shattered at the Tête-à-Tête Café on Avenue Z, which Berke described as “basically a fish tank,” filled to the waist with water. Cars were submerged, leaving them coated with mud by morning.

One most infuriating things, Berke says, was that all the talk on radio and television was about Manhattan.

“There wasn’t a word of southern Brooklyn, and from what I’ve seen, there still is none. I understand the Financial District and Lower Manhattan are important areas, but you’ve got tens of thousands, maybe hundreds of thousands of people down here who are in a really tough spot now.”

Sandy also forced the evacuation of coastal communities in Massachusetts while authorities in Maine shut down the Port of Portland.

Earlier Monday off the North Carolina coast, the tall ship HMS Bounty sank; 14 crew members were rescued by the Coast Guard, but one crew member drowned and the captain was missing.

Colum Lynch and Suzanne Sataline in New York, and Frederick Kunkle, Laura Vozzella, Jeremy Borden, Lynh Bui, Ann E. Marimow, Lori Aratani, Emma Brown, Tim Craig, Aaron C. Davis, Hamil R. Harris, Sally Jenkins, Ed O’Keefe, Del Quentin Wilber and Debbi Wilgoren in Washington, contributed to this report.