Two days after the superstorm Sandy struck the East Coast, rescue officials confronted flooded cities and battered beach towns that remained dangerous and chaotic, particularly in pockets of hard-hit New Jersey.

Large portions of this old factory city were still flooded, and pumps were working round-the-clock to clear a toxic and potentially deadly mix of water, oil and sewage estimated at more than 500 million gallons. National Guard troops in 2.5-ton Humvees patrolled the flooded streets, seeking to evacuate the most vulnerable of the city’s 20,000 stranded residents, nearly half of Hoboken’s population, who were told to stay inside and signal for help with pillowcases.

Mayor Dawn Zimmer stood in the gathering darkness Wednesday afternoon and begged the outside world to speed more supplies, such as flashlights, batteries, food, generator fuel and drinking water.

“We ask anyone who’s listening to deliver supplies to us,” she said from the steps of City Hall, which was without power.

The mayor spoke over the sound of whirring water pumps and humming diesel generators. The smell of sewage, seeping up from storm drains, hung in the air on some of the city’s streets.

“If people who are listening have generators, we are asking you to bring them,” Zimmer said. “We are still very much in crisis mode.”

The U.S. death toll from Sandy had risen to at least 75 by Thursday, the Associated Press reported, with the largest number of fatalities — 30 — occurring in New York. Many sections of New York City remained dark, but parts of the subway began running again Thursday, and three of seven tunnels under the East River had been cleared of water.

Police enforced mandatory carpooling, with at least three people required in each car heading into Manhattan. Traffic remained heavy. All three major New York-area airports had reopened for business.

Across the Hudson River in New Jersey, state officials reported at least 14 dead, AP said. But the scope of the damage, which ran from beach communities to aging cities, appeared to dwarf that of New York.

President Obama got a firsthand look at the devastation when he joined New Jersey Gov. Chris Christie (R) on Wednesday for a helicopter tour of the state’s ravaged beach communities.

From his Marine One helicopter, the president looked down on boardwalks smashed to splinters by the storm, houses split open by floodwater and the ruins of a roller coaster that had come unmoored from a shattered pier in Seaside Heights, N.J., and washed into the ocean.

“I want to just let you know that your governor is working overtime to make sure that as soon as possible, everybody can get back to normal,” Obama told residents in the seaside community of Brigantine after the tour. “The entire country has been watching what’s been happening. Everybody knows how hard Jersey has been hit.”

The state’s coastal barrier islands were decimated by high winds and water that knocked homes from their foundations, flooded streets and ruptured natural gas lines, which continued to burn Wednesday in some New Jersey beachfront communities, such as Brick Township.

More than a dozen homes were destroyed in the shore town of Mantoloking when stubborn floodwater prevented firefighters from reaching blazes sparked by the natural gas leaks, the Associated Press reported.

Large swaths of the state were still without power. Lines stretched for blocks at the few open gas stations around Toms River, N.J, scene of some of the worst flooding. Police blocked bridges leading to barrier islands where hundreds of homes were under water. School buses carrying evacuees passed a small yacht in the middle of the road.

There were some signs of progress in the recovery effort. Local power company officials, aided by crews from nine states, estimated that they had restored electricity to about 500,000 New Jersey residents. For some, though, the wait for power was expected to stretch as long as 10 days.

There were no reports of widespread looting in the state.

Hoboken residents in some of the more heavily flooded neighborhoods trickled out of their homes — knapsacks, duffel bags, children and dogs in tow — heading by foot to drier land in Jersey City.

Thousands of other Hoboken residents stayed either because they had nowhere to go or because getting out was too difficult. They wandered the streets or drifted toward the handful of working generators so they could charge their cellphones and try to reestablish a connection with the outside world. The historic clocks that line Washington Street, the main thoroughfare, all showed the time as 9:03 p.m., when the city lost power Monday.

This once-gritty industrial city has become a haven for younger professionals seeking a cheaper alternative to Manhattan. In Hoboken’s neighborhoods, they mix with immigrants and older residents who came to the city decades earlier to work in its factories.

Inside the darkened City Hall, built in the 19th century, a volunteer operation took shape, with young people lining up to pick up flashlights and addresses where older residents might need help.

“Can I have the Spanish-speaking people raise their hands,” a volunteer coordinator shouted. “It is very hectic right now.” She warned them to be careful if they were compelled to wade into water above their knees.

The volunteers became the first contact for many stranded residents.

“Good afternoon. Can I have your attention, please?” volunteer Tom O’Connor called into a loudspeaker in the lobby of a Bloomfield Street apartment building whose residents were elderly people on fixed incomes.

O’Connor, an international sales consultant, had come to ensure that the building’s water was still potable and available on the higher floors. Many residents were furious at the conditions in the building.

“The elevators are dark,” said Frank Bongiorno, 80, who walked down 13 flights of stairs to the flooded street in search of somewhere to charge his cellphone. “We’ve got a lot of people on respirators here. Why are they doing this?”

National Guard Humvees ferried evacuees to City Hall, from which residents were taken to shelters or were able walk to Jersey City to find friends or relatives who could take them to a safer, drier place.

Wilbert Rivera, who has survived on disability for four years, sat on the curb near City Hall. The 46-year-old native Puerto Rican rolled up his right pant leg to show a swollen knee and complained that he was in pain. He and his neighbors finally got through on 911 late Wednesday afternoon, and the National Guard rescued him from his flooded block.

“Gout,” he said, pointing to his throbbing leg. “Waiting to hospital, please.”

Jaffe reported from Washington. Alice Crites in Washington and Carol Morello in Toms River contributed to this report.