Irene batters New York, raising fears of flooding
Seawater surged into flood-prone areas of New York on Sunday as Tropical Storm Irene hit the city, downgraded from a hurricane but still bringing fierce winds and rain.
Some 370,000 people were ordered to evacuate and streets are eerily quiet, a BBC correspondent says.
At least 11 deaths have been linked to the powerful storm.
Irene has already destroyed buildings in North Carolina and Virginia, and left millions without power.
The storm was classified as a hurricane when it swept through the Caribbean last week. Despite the downgrade to a tropical storm, it has still been destructive and disruptive. It is expected to hit Canada on Sunday night.
US Homeland Security Secretary Janet Napolitano said that while there was still a way to go with Irene, the "worst of the storm has passed", adding that the precautions taken had "dramatically decreased" the threat to lives along the eastern US.
But National Hurricane Center director Bill Read warned that heavy rains meant there was still a major flooding risk to river systems, especially in New England.
The BBC's Laura Trevelyan, in New York's Battery Park, says the city felt the full force of the storm, whose arrival coincided with a high tide.
The centre of the hurricane moved over New York City at about 09:00 (13:00 GMT), the National Hurricane Center said. The centre is now inland over southeastern New York state.
Some 370,000 people living in low-lying areas of New York City had been told to leave, and the city's public transport system has been closed.
Our correspondent said a feared storm surge affecting New York's Hudson River, was about 5ft (1.5m) high and there are concerns that floodwaters may affect underground New York - its subway system and the network of cables that power the city.
Ocean water has streamed into streets in New York's Queens district, while streets in Brooklyn's Coney Island were also under water. In Manhattan, water from New York Harbour lapped onto pavements in Battery Park, and about 1ft of water washed over the wall of the marina in front of the New York Mercantile Exchange.
Hours earlier, the then Hurricane Irene came ashore in New Jersey, about 100 miles (160km) to the south, where state Governor Chris Christie said he expected the cost of repairing damage to be "in the billions of dollars, if not in the tens of billions of dollars".
Irene has also dumped more than 1ft (30cm) of rain on North Carolina and Virginia, and there were reports of storm surges of nearly 10ft.
The north-eastern seaboard is the most densely populated corridor in the US. More than 65 million people live in major cities from Washington DC in the south to Baltimore, Philadelphia, New York and Boston further north.
States of emergency were declared in North Carolina, Maryland, Virginia, Delaware, New Jersey, New York and Connecticut. New York's John F Kennedy and LaGuardia airports, and Newark in New Jersey, have shut, with the cancellation of at least 10,000 flights.
While international airports will reopen on Monday afternoon, disruption is likely to extend to later in the week.
Pennsylvania Governor Tom Corbett warned that while the storm may be weakening, there was still danger ahead. "The rivers may not crest until Tuesday or Wednesday. This isn't just a 24-hour event," he said.
At least 11 people are now known to have died during the storm, with as many as 4.5 million people affected by power cuts, reports say. Most of those who died were killed either by falling trees, or in accidents relating to the sheer amount of water on the streets.
President Barack Obama cut short his holiday to Martha's Vineyard to co-ordinate efforts to deal with the storm and on Sunday held a video conference for an update on the response to the storm.
Correspondents say the president is very keen to avoid any criticism that surrounded the federal government's response to Hurricane Katrina six years ago.
Samantha Mair, a Briton who lives in Manhattan, stayed in her apartment, but went out on the streets and found them "extremely wet".
"There's water everywhere, as people are trying to move it out of their houses and onto the streets, they're trying to get it down the drains but the drains aren't handling it very well," she told the BBC.
"This is my first time witnessing anything like this," student Ryan Narcisse of Roselle, New Jersey, told the BBC. "The street was blanketed with a sheet of water...