Hurricane Irene has claimed 44 lives, and the death toll could rise as it threatens to batter America’s Northeast coast again.

About 5.1 million households and businesses are without electricity all the way from North Carolina to Maine and it could take days, or even weeks in more remote areas before it is restored.

New York City, which was braced for urban disaster, was relatively spared by Hurricane Irene, which was downgraded to a tropical storm when it arrived.

 Irene weakened to winds of 60 mph, well below the 74 mph dividing line between a hurricane and tropical storm. Under its first hurricane warning in a quarter-century, New York, the US’s largest city had taken extensive precautions. There were sandbags on Wall Street, tarpaulins over

subway grates and plywood on storefront windows. The subway stopped rolling. Broadway and baseball were cancelled.

Still, the storm unleashed furious wind and rain on the city on Sunday and sent seawater surging into the Manhattan streets. About 100,000 in the city are still without power, the hurricane shattered skyscraper windows and there is severe flooding.

A foot of water rushed over the wall of a marina in front of the New York Mercantile Exchange, where gold and oil are traded, and floodwater lapped at the wheel wells of yellow cabs.

"You could see newspaper stands floating down the street," said Scott Baxter, a hotel doorman in the SoHo neighborhood.

As the storm marched into New England, though, authorities in its wake cautiously expressed relief.

Life and public transport in New York City, including the subway, is now running to schedule after being shut down in an unprecedented safety move.

In the north, the State of Vermont sustained the most serious flooding, to a level is has not seen in 100 years. New Jersey also reported widespread damage.

Hurricane Irene moved on Monday to the Canadian East Coast as a tropical storm with wind gusts up to 90 km/h. More than 165,000 people in Quebec are currently without power.

Air traffic on the US East Coast is also returning to normal after 12,000 flight cancelations between Friday and Sunday, and an estimated $300m worth of losses between the US’s 10 largest airlines.

But experts still warn of danger, as the storm passes by the Northeast. Rivers could crest after the skies the clear, and the ground in most of the region is saturated from a summer of persistent rain.

Max Mayfield, former director of the National Hurricane Centre, said the storm wasn't just a lot of hype with little fury. At least 2.3 million people were given orders to evacuate (though it was not clear how many obeyed them), and Mayfield praised authorities, from meteorologists to emergency managers at all levels, for taking the threat seriously.

"They knew they had to get people out early," Mayfield said. "I think absolutely lives were saved."

As the East Coast cleans up, it can't afford to get too comfortable. Off the coast of Africa is a batch of clouds that computer models say will probably threaten the East Coast 10 days from now, Mayfield said. The hurricane centre gave it a 40 percent chance of becoming a named storm over the next two days.

"Folks on the East Coast are going to get very nervous again," Mayfield said.

The National Hurricane Centre said the eye of the huge storm reached land near Little Egg Inlet, N.J., at 5.35am. The eye previously reached land Saturday in North Carolina before returning to the Atlantic, tracing the East Coast shoreline.

Of the 14 deaths, at least nine were caused by falling trees or car crashes into trees. The victims included five in North Carolina, four in Virginia, one each in Maryland, New Jersey and Connecticut, and two in rough surf in Florida.

Irene 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 on Aug. 29, 2005. Experts said that probably no other hurricane in American history had threatened as many people.