A weakened but still dangerous Hurricane Irene shut down New York and menaced other cities more accustomed to snowstorms than tropical storms as it steamed up the East Coast on Saturday, unloading 30 cm of rain on North Carolina and Virginia and knocking out power to two million homes and businesses.

New York emptied its streets and subways and waited with an eerie quiet. Washington braced for the onslaught, too, as did Philadelphia, the New Jersey shore and the Boston metropolitan area. Packing wind gusts of 185 km/h, the hurricane had an enormous wingspan — 805 kilometres — and threatened a swath of the nation inhabited by 65 million people.

The hurricane stirred up two-metre waves, and forecasters warned of storm-surge danger on the coasts of Virginia and Delaware, along the Jersey Shore and in New York Harbor and Long Island Sound. Across the Northeast, drenched by rain this summer, the ground is already saturated, raising the risk of flooding as well as the danger of trees falling onto homes and power lines.

Irene made its official landfall just after first light near Cape Lookout, N.C., at the southern end of the Outer Banks, the ribbon of land that bows out into the Atlantic Ocean. While it was too early to assess the full extent of damage, shorefront hotels and houses were lashed with waves, two piers were destroyed and at least one hospital was forced to run on generator power.

The storm knocked out power and piers in North Carolina, and clobbered Virginia with wind as it churned up the coast toward major urban centres in the U.S. Northeast.

No longer safe to be outside

New York City's mayor, Michael Bloomberg, said late Saturday night that it was not longer safe to be outdoors and that the edges of Hurricane Irene are reaching the city.

In Washington, D.C., tension was rising as the nation's capital awaited its first hurricane in more than a half-century, a storm that could test its ability to protect both national treasures and its many poor and vulnerable neighbourhoods.

With most of its transportation machinery shut down, the Eastern Seaboard spent the day nervously watching the storm's march across a swath of the nation inhabited by 65 million people.

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Virginia Beach visitors point out the waves as Hurricane Irene approaches the region in Virginia Beach, Va., Saturday. (Steve Helber/Associated Press)

At least 2.3 million were under orders to move to somewhere safer, although it was unclear how many obeyed or, in some cases, how they could.

CBC weather specialist Jay Scotland, who is tracking Irene, said the storm has been weakening as it's been drawing in dry air from the west, but that the hurricane is now moving back over water.

"This is the issue for New York," Scotland said. "That easterly component to the wind continuing overnight, increasing to tropical-storm force, and by 6 a.m. tomorrow, that will be hurricane-force wind interacting with New York."

Storm surges, coastal flooding, torrential rain and very powerful winds are to be expected.

Storm surged feared

The hurricane's outer reaches stretch from the Carolinas to Cape Co, Mass., and it has been blamed for at least six deaths, with some reports saying the current death toll has rised to eight. A North Carolina man was struck by a flying tree limb, someone in Virginia was killed when a tree fell on a car, and an 11-year-old boy in Virginia died when a tree crashed through his apartment building.

"Things are banging against the house," Leon Reasor said as he rode out the storm in the town of Buxton. "I hope it doesn't get worse, but I know it will. I just hate hurricanes."

By afternoon, the storm had weakened to sustained winds of 120 km/h, down from 160 km/h on Friday. That made it a Category 1, the least threatening on a one-to-five scale, and barely stronger than a tropical storm. Its eye was positioned almost exactly where North Carolina meets Virginia at the Atlantic, and it was moving more slowly, at 17 km/h and back out toward the ocean.

After the Outer Banks, the storm strafed Virginia with rain and strong wind. It covered the Hampton Roads region, which is thick with inlets and rivers and floods easily, and chugged north toward Chesapeake Bay. Shaped like a massive inverted comma, the storm had a thick northern flank that covered all of Delaware, almost all of Maryland and the eastern half of Virginia.

It was the first hurricane to make landfall in the continental United States since 2008, and came almost six years to the day after Katrina ravaged New Orleans. Experts guessed that no other hurricane in American history had threatened as many people.

Defence Secretary Leon Panetta told 6,500 troops from all branches of the military to get ready to pitch in on relief work, and President Barack Obama visited the Federal Emergency Management Agency's command centre in Washington to offer moral support.

"It's going to be a long 72 hours," he said, "and obviously a lot of families are going to be affected."

In New York, authorities began the herculean job of bringing the city to a halt. The subway began shutting down at noon, the first time the system was closed because of a natural disaster. It was expected to take as long as eight hours for all the trains to complete their runs and be taken out of service.

'Time to leave is now'

On Wall Street, sandbags were placed around subway grates near the East River while tarps were placed over other grates. Construction stopped throughout the city, and workers at the site of the World Trade Center dismantled a crane and secured equipment.

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This NOAA satellite image taken Saturday at 4:45 a.m. ET shows a swirl of clouds off the East Coast of the United States associated with Hurricane Irene as it is about to make landfall along the Outer Banks of North Carolina. (Weather Underground/Associated Press)

While there were plenty of cabs on the street, the city was far quieter than on an average Saturday. In some of the busiest parts of Manhattan, it was possible to cross a major avenue without looking, and the waters of New York Harbour, which might normally be churning from boat traffic, were quiet before the storm.

The biggest utility, Consolidated Edison, considered cutting off power to 6,500 customers in lower Manhattan because it would make the eventual repairs easier. Mayor Michael Bloomberg also warned New Yorkers that elevators in public housing would be shut down, and elevators in some high-rises would quit working so people don't get trapped if the power goes out.

"The time to leave is right now," Bloomberg said at an outdoor news conference at Coney Island, his shirt soaked from rain.

A day earlier, the city ordered evacuations for low-lying areas, including Battery Park City at the southern edge of Manhattan, Coney Island with its famous amusement park and the beachfront Rockaways in Queens.

The five main New York-area airports — La Guardia, John F. Kennedy and Newark, plus two smaller ones — brought in their last arriving flights around noon. The Giants and Jets postponed their preseason NFL game, the Mets postponed two baseball games and Broadway theaters were dark.

For all the concern, there were early signs that the storm might not be as bad as feared. Some forecasts had it making landfall as a Category 3 storm and perhaps reaching New York as a Category 2.

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People run from the beach in Kitty Hawk, Outer Banks, N.C., Saturday, as Hurricane Irene reaches the North Carolina coast. (Charles Dharapak/Associated Press)

"Isabel got 10 inches [25 cm] from coming in the house, and this one ain't no Isabel," said Chuck Owen of Poquoson, Va., who has never abandoned his house to heed an evacuation order. He was referring to Hurricane Isabel, which chugged through in 2003.

Still, Owen put his pickup truck on a small pyramid of cinder blocks to protect it from the storm tide, which had already begun surging through the saltwater marshes that stand between Poquoson and Chesapeake Bay.

Travellers stranded

Airlines said 9,000 flights were cancelled, including 3,000 on Saturday. Airlines declined to say how many passengers would be affected, but it could easily be millions because so many flights make connections on the East Coast. There were more than 10,000 cancellations during the blizzard last winter.

American Airlines spokeswoman Andrea Huguely said it was not clear when flights would resume out of New York.

Greyhound suspended bus service between Richmond, Va., and Boston. Amtrak cancelled trains in the Northeast for Sunday.

The power losses were heavily concentrated in Virginia and North Carolina, where Irene charged ashore early Saturday morning. Dominion Resources reported almost 600,000 customers without power and Progress Energy 260,000, with much of the outages in Wilmington and Wrightsville Beach, N.C.

'Don't wait, don't delay': Obama

"Don't wait, don't delay," said President Barack Obama, who decided to cut short his summer vacation by a day and return to Washington on Friday. "I cannot stress this highly enough: If you are in the projected path of this hurricane, you have to take precautions now."

Wind and rain knocked out power to more than 91,000 customers along the North Carolina coast, including a hospital in Morehead City. A woman who answered the phone there said the hospital was running on generators.

Hurricane warnings were issued from North Carolina to New York and farther north to the islands of Nantucket and Martha's Vineyard off Massachusetts. Evacuation orders covered at least 2.3 million people, including 1 million in New Jersey, 315,000 in Maryland, 300,000 in North Carolina, 200,000 in Virginia and 100,000 in Delaware.

"This is probably the largest number of people that have been threatened by a single hurricane in the United States," said Jay Baker, a geography professor at Florida State University.

Airlines are scrapping more than 8,300 flights this weekend from North Carolina to Boston, grounding passengers as Irene sweeps up the East Coast. There were more than 3,600 cancellations on Saturday alone.

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Coney Island resident Orlando Perez, with bags, and Adrian Espinoza, in background preparing window covers, get ready to evacuate the Coney Island section of New York Saturday. (Craig Ruttle/Associated Press)

All New York City-area airports closed to arriving flights at noon on Saturday. Ronald Reagan Washington National Airport and Washington Dulles International Airport were both open as of noon, but most flights had been cancelled.

Train and bus service is also extremely limited as both Greyhound and Amtrak suspended or limited service along the eastern corridor.

A total of 11 states, including New York, have declared a state of emergency.

Berms being built

The CBC's David Common is in Long Beach, New York, where the surf is starting to pick up and they're building berms to absorb the sea surge when it comes ashore overnight and Sunday.

The city is part of the mandatory evacuation zone that affects about 377,000 people who live in flood-prone areas, including Battery Park City at the southern tip of Manhattan, Coney Island and the beachfront Rockaways.

"Not everybody's going to leave and the police aren't going to force them," Common said. "But the message is that if you can't leave or aren't going to leave, then they want you to write your name and your next-of-kin's name on an index card and put it in your left shoe. That probably gets the idea across, doesn't it?"

Many gas stations have run dry as people have stocked up on fuel, as well as food and water, anticipating shortages. Widespread power outages are also expected.

"Of course everybody's going for worst-case scenario: try to prepare for the worst and hope for the best," Common said. "That's the mentality, and the phrase, if there is one, in New York City is, 'Get a kit, make a plan.'"

New York City officials started to shut down the mass transit system at noon, ahead of Hurricane Irene, the first time it's been closed because of a natural disaster.  They say it will take about eight hours before the system will be shuttered.

It won't reopen until at least Monday, after pumps remove water from flooded stations. Even on a dry day, about 15 million litres of water are removed from the tunnels deep underground.

The transit authority says the systems can't operate in sustained winds higher than 62 km/h and say shutting down is a precaution.

Mayor Bloomberg urged New Yorkers who needed to leave to get out right away because the city does not have enough resources to evacuate the majority of affected residents after the weather worsens, he said.

"Staying behind is dangerous, staying behind is foolish, and it's against the law, and we urge everyone in the evacuation zones not to wait until gale-force winds," he said at a news conference from Coney Island. "The time to leave is right now."

With files from CBC News