The most powerful hurricane to threaten the Eastern Seaboard in almost two decades hit the Washington region Saturday, bringing heavy rains and high winds that plunged homes into darkness, turned trees into projectiles and caused at least eight deaths.

Early Sunday morning the storm’s toll in damage and outages continued to rise in the Washington area. Evacuations were underway in St. Mary’s County as water rose behind a dam at St. Mary’s Lake. There was damage reported to at least two buildings in the District, one of them at Georgetown University.

As winds appeared to be rising after midnight, the number of outages reported by Baltimore Gas and Electric alone jumped to nearly 300,000. More than one third of them were in Anne Arundel County.

Increasing numbers of fallen trees were reported in at least two jurisdictions, the District and Prince George’s County.

After making landfall in North Carolina, with gusts up to 115 mph, Hurricane Irene continued its fierce and relentless march north toward New York City and New England. Governors and mayors spent much of Saturday pleading with people to get out of the storm’s way.

The storm arrived at day’s first light, at a point appropriately named Cape Lookout on the Outer Banks. As the hurricane spread beyond North Carolina, the most densely populated stretch in the country all but ground to a halt.

Airlines canceled 9,000 flights along the East Coast, Amtrak stopped all trains from Boston south and Greyhound suspended bus service between Richmond and Boston for the rest of the weekend. Capital Bikeshare halted all bike rentals in the District.

The subway stopped running in New York City. The three airports serving the Washington area remained open Saturday evening, but most flights had been scratched. The Chesapeake Bay Bridge was closed at 7:35 p.m. because of severe winds and unsafe driving conditions.

Power outages increased by the hour as winds toppled trees and power lines. More than 980,000 residential and business customers of Dominion Power were without electricity early Sunday in Virginia and North Carolina, the company reported. The Richmond area and southeastern Virginia were hit hardest. At 2 a.m. Sunday the figure in Dominion’s northern Virginia region was about 86,000.

Pepco’s outage numbers rose about 180,000 around 2 a.m. Sunday.

Of BGE’s nearly 300,000 outages, most were reported in Anne Arundel County and Prince George’s County, with 94,000 and 21,000 customers affected, respectively.

At one point, tens of thousands of customers of the Southern Maryland Electric Cooperative were without power, a large number in St. Mary’s County.

Outages were increasing in Maryland on Sunday morning as the storm drove north along the coast of the Delmarva region.

“This is a very dangerous time,” Virginia Gov. Robert F. McDonnell said around 8 p.m., warning there could be tidal flooding in Hampton Roads with a storm surge of at least eight feet.

Early this morning wind gusts in the Washington area continued to rise above 40 mph.

Three deaths in Virginia were among at least seven that were linked to the storm. An 11-year-old boy died in Newport News when a tree fell on his apartment. The Newport News Daily Press reported that he was in bed beside his mother, who was not injured. Falling trees also caused the deaths of two other people in Brunswick and Chesterfield counties, though no details were available.

A death was reported in the Queenstown area of Queen Anne’s County in Maryland. Kevin Aftung, the county’s chief of emergency services, said a tree fell on a chimney of a house and the resulting damage caused fatal injuries to a woman inside.

The full extent of the storm damage won’t be known until after the hurricane weakens, sometime late Sunday.

In Norfolk, as Irene heralded itself with sheets of rain and howling gusts of wind that peaked around 60 mph, a massive water main break on a city street erupted about 4 p.m. and sprayed water like a geyser at least 30 feet in the air. WAVY Channel 10 news reported that some residents had no water, particularly in low-lying areas of the city.

Even before Irene made landfall, President Obama signed emergency declarations for nine states, allowing the federal government to pay some costs and assist in cleanup.

Cities up and down the East Coast were particularly vulnerable to its fury.

Houses in Virginia Beach were sliced open, and some empty homes were looted.

And in New York City, where 370,000 people were ordered to evacuate, the city girded for the storm’s crippling impact. Mayor Michael R. Bloomberg warned that high-rise buildings were likely to suspend elevator service so that no one would be trapped during a power outage. A storm surge is likely to send water streaming through the streets of Lower Manhattan and Wall Street, and electricity would be cut before that happens.

Officials had been making increasingly dire predictions about Irene for days, and even veterans of other hurricanes scrambled to get out of the storm’s path.

More than 2 million people were ordered to evacuate along the coast, and some shelters were overwhelmed.

McDonnell said that more than 3,000 people have been taken in at 74 shelters around Virginia. Two dozen are in Hampton Roads alone.

In the Washington region, Montgomery and Prince George’s counties each opened two shelters for displaced residents. In the District, three shelters opened and recreation centers and schools were on standby to be turned into shelters if needed.

Hampton Roads served as an early warning of the storm’s strength, even though it had been downgraded a notch to a Category 1 hurricane.

Five homes were severely damaged in the Sandbridge Beach area south of the city — with the roofs blown off two and collapsed walls in others — in what fire officials suspect was a small tornado or strong microburst, said Battalion Chief Tim Riley of the Virginia Beach Fire Department. The homes were empty because occupants had heeded the mandatory evacuation order, he said.

Police vehicles swarmed into the area after several people reported looters in the damaged homes. Two people were arrested, accused of looting in the area, said city spokeswoman Mary Hancock. More details were not available.

Dave Smith, 58, a retired salesman, said he was not evacuating because he feared looting. “I’m not leaving my stuff. And that’s the reason I stayed — people are breaking into houses,” Smith said.

As the storm crept north, 500 miles wide at its core, it seemed to grow more menacing.

In Rehoboth Beach, where streets began to flood by 4:30 p.m., it was difficult to see more than 150 yards on the beach by late afternoon. A stinging rain fell as winds blew foam and sand onto the boardwalk.

Many residents awoke to warnings at 7:15 a.m., when a storm siren echoed through the streets. It was followed by an announcement that the city was under mandatory evacuation, calling for residents to leave the coastal area as soon as possible.

“It scared the [heck] out of me,” said Al Morris, who has been coming to Rehoboth for 40 years.

The alarm, spread by loudspeakers positioned around town, sounded two more times before nightfall as winds blew a thick layer of sand onto the boardwalk. Large sections of roadways were covered in standing water.

Due to the worsening conditions, Delaware Gov. Jack Markell (D) announced a driving ban in Sussex, Kent and New Castle counties. McDonnell said the Virginia National Guard has been mobilized, and he has authorized local jurisdictions to impose overnight curfews. Several Hampton Roads jurisdictions, including Newport News, have done so.

With beach communities in Virginia, Maryland and Delaware largely evacuated, people living inland in Eastern Shore communities began to receive the same message.

“We are supposed to evacuate in a few hours now,” Sabine Boggs said. “Salisbury City police drove down our street with lights flashing and a PA system announcement that a shelter has been set up at the civic center. All the garden furniture is stuffed in our sunroom, and the treadmill has become a good plant stand.”

Even as the winds toppled stop signs and pushed slender trees nearly horizontal, authorities had to coax thrill-seekers away from the beaches. They issued dire warnings to residents stubbornly staying behind that they would not be rescued.

A team of city police, beach patrol officers and Maryland state troopers took the names of next of kin from about 300 Ocean City residents who refused to budge. They would be on their own, they were told.

Lifeguards ordered daredevil surfers to get out of the water as winds reached gale force.

Even as winds began to break branches and bend street signs, some people ventured out to experience the leading edge of the hurricane. Ocean City police officer Freddie Howard, five hours into what he expected to be a 48-hour shift, was patrolling near 45th Street when he saw two figures careening unsteadily on bicycles.

Catching up to them in the breezeway of a condominium tower, Howard flipped his police lights on and forced his cruiser door open against the gale.

“What are you doing out here?” he shouted over the roar. The two men, in their early 20s, could barely hold their bikes upright, although one of them never stopped filming Howard and his flashing patrol car.

“We’re just looking around,” one man shouted back.

“That’s not a good idea,” the officer said. “We’re evacuating the town. You should go for your own safety.”

But the two insisted that they would be fine in their condo, so Howard let them go.

Willie Long, a U.S. Postal Service mail carrier in Virginia Beach, went about his usual rounds, though wetter than usual, somewhat to the surprise of residents. “They have two views: One is, ‘You’re crazy.’ The other is, ‘Kudos,’ ” Long said.

And near Annapolis, Michael Marvin, who moved from the District to within 100 feet of the Chesapeake Bay just days before Hurricane Isabel hit in 2003, hunkered down as the day’s grayness turned to dusk Saturday.

“Fill the tubs, replace the batteries, clear the outside drains, charge the phones and wait,” Marvin said at his home just north of Annapolis.

The scenarios officials had been warning about for days seemed to be coming true. By 6 p.m., winds exceeded 50 miles an hour in Ocean City. Officials pulled police patrols off the streets and ordered officers into safe staging areas around town.

“We’ll assess calls on a case-by-case basis,” said Ocean City communications director Donna Abbott. “Otherwise, we’ll keep them in until the winds die down and it’s safer to be out.”

The lower, southernmost blocks of the island were beginning to flood, Abbott said. They city also shut down its waste water treatment facilities.

Staff writers Carol Morello, Clarence Williams, Martin Weil, Ashley Halsey III, Miranda S. Spivack, Nikita Stewart, Brian M. Rosenthal, Anita Kumar, John Wagner, Robert Samuels and Mary Pat Flaherty contributed to this report.