Much of New York has been plunged into darkness by superstorm Sandy, which has killed at least one person in the city, flooded its waterfront, financial district and subway tunnels and cut power to nearly a million people.
The Empire State Building remained an eerie beacon of light as 250,000 Manhattan homes were deprived of power, while emergency officials confirmed at least one 30-year-old man had died, killed by a falling tree in Queens.
The East River and the Hudson River flooded subway and car tunnels and several feet of seawater swamped into Battery Park at the foot of Lower Manhattan, with waters rising and the rain showing no sign of abating.
"Lower Manhattan is being covered by seawater. I am not exaggerating. Sea water is rushing into the Battery Tunnel," said Howard Glaser, director of operations for the New York state government.
The Battery Tunnel is a road tunnel linking the south end of Manhattan, New York's financial center, to Long Island under the East River.
Local energy supplier Con Edison reported that 250,000 customers had lost power in Manhattan alone.
In addition to the surging waters of the East and Hudson rivers, the city was by battered by what the National Weather Service called "hurricane-force gusts" of more than 90 miles per hour (145 kilometers per hour).
As the evening tide hit its height the storm surge was a record 13.7 feet (4.2 meters). Before Hurricane Sandy made landfall, forecasters had warned than any more than 11 feet could cause catastrophic flooding.
Cars could be seen afloat in several Manhattan streets, and the facade of a six-story building collapsed.
Local broadcaster WNBC said some houses on Staten Island were "flooded up to their attics," while the New York police department sought boats to conduct rescue missions there and on Brooklyn's Coney Island.
Floods swamped cars in Brooklyn, while fierce gusts pushed over a crane on a Manhattan skyscraper -- leaving it dangling perilously atop the 90-story luxury apartment.
The boom of the crane swayed in the fierce gusts over streets near Central Park that police and fire services evacuated because of the risk that it could fall.
Gas and water pipes at street level were closed and city engineers and fire department experts climbed the 1,004-foot (306-meter) building to assess the danger.
In another spectacular demonstration of its power, the hurricane pulled off the facade of a three-story building in the Chelsea district. Again no injuries were reported.
Tens of thousands of people ignored appeals by New York Mayor Michael Bloomberg to leave the districts at risk.
"If water is coming into your home, go to the highest area," Bloomberg advised citizens as he held a hastily-arranged press conference amid the worst of the carnage.
"It's still very dangerous and from now until the storm is well passed you just have to shelter in place. You need to stay wherever you are. Let me repeat that. You have to stay wherever you are."
New York authorities had earlier closed the subway train system and nearly all tunnels and bridges that take traffic off Manhattan as the full force of Sandy hit America's biggest city.
With Wall Street closed for the first time since the September 11, 2001 attacks and the city at a near standstill, police went to several districts with loud speakers and special buses trying to persuade people to move.
New York state also called up more than 2,100 National Guard troops on Sunday and Monday to patrol threatened districts.
Authorities issued a mandatory evacuation order for 375,000 people at risk from a storm surge predicted to be over 11 feet (3.5 meters), but the majority decided to brave it out.
As night fell, Bloomberg had warned that it may be too late to get away.
On the streets of Manhattan, police cars used to block streets gradually retreated as flood water moved further into the island.
Schools and landmark attractions such as the Empire State Building were all closed and were to stay closed Tuesday. Hardly a car ventured onto the streets.
Earlier, Sandy slammed into the New Jersey coastline and hurled a record-breaking 3.9-metre surge of seawater at New York City, roaring ashore after washing away part of the Atlantic City boardwalk.
Just before its centre reached land, the storm was stripped of hurricane status but the distinction was purely technical, based on its shape and internal temperature.
It still packed hurricane-force wind, and forecasters were careful to say it remained every bit as dangerous to the 50 million people in its path.
The National Hurricane Center announced at 8pm on Monday (1100 AEDT Tuesday) that Sandy had come ashore near Atlantic City.
The sea surged a record of nearly four metres at the foot of Manhattan.
In an attempt to lessen damage from the storm, New York City's main utility cut power to about 6500 customers in lower Manhattan.
Authorities worried that seawater would seep into the New York subway and cripple it, along with the electrical and communications systems that are vital to the nation's financial centre.
As it closed in, Sandy knocked out electricity to more than 1.5 million people and figured to up-end life for tens of millions more.
It smacked the boarded-up big cities of the Northeast corridor, from Washington and Baltimore to Philadelphia, New York and Boston, with stinging rain and gusts of more than 135km/h.
As it made its way toward land, it converged with a cold-weather system that turned into a fearsome superstorm, a monstrous hybrid consisting not only of rain and high wind but of snow.
Forecasters warned of six metre waves bashing into the Chicago lakefront and up to 0.9 metres of snow in West Virginia.
The storm had already killed at least 67 people in the Caribbean as it came north, and American rescue services were braced for more casualties.
Authorities warned the threat to life and property was "unprecedented" and ordered hundreds of thousands of residents in cities and towns from New England to North Carolina to evacuate their homes and seek shelter.
Shortly after 7.00 pm (2300 GMT), the National Hurricane Center said wind speeds inside Sandy had dropped slightly as the storm became a post-tropical cyclone, but remained hurricane-force at around 85 miles per hour (140 kph).
THOUSANDS OF TRAVELERS STRANDED
Falling trees dragged down power cables, plunging millions of homes into darkness as night fell, while storm warnings cut rail links and marooned tens of thousands of travelers at airports across the region.
In New York, bystanders were awestruck as a massive tower crane snapped and dangled precariously from a skyscraper above a Manhattan street.
The storm, a deadly combination of a rain-sodden post-tropical cyclone rolling north from the Caribbean and fierce wintry winds approaching from Canada, had been expected, but gained speed and fury even as it made landfall.
While the coast faced the storm surge and heavy rain normally associated with hurricanes, this "Frankenstorm" hybrid system triggered massive early snowfalls in the mountains of West Virginia and North Carolina.
"Hurricane-force winds are expected to gradually spread across southern New England and mid-Atlantic states from Connecticut southwards to New Jersey and Delaware," the National Hurricane Center warned.
"The combination of an extremely dangerous storm surge and the tide will cause normally dry areas near the coats to be be flooded by rising waters."
Barometric pressure in the heart of the storm dropped to only 940 millibars, on course to break records for low pressure in the region.
"The most important message to the public I have right now, is 'please listen to what your state and local officials are saying.' When they tell you to evacuate, you need to evacuate," President Barack Obama said.
'$20 BILLION' WORTH OF DAMAGES
Disaster estimating firm Eqecat forecast that Sandy would affect more than 60 million Americans, a fifth of the population, and cause up to $20 billion (15 billion euros) in damage.
Refineries closed and major arteries such New York's Holland Tunnel were shut to traffic. The operator of two major New Jersey nuclear plants said they might have to be closed, threatening half the state's power supply.
The New York Stock Exchange, the Nasdaq and the futures markets in Chicago were closed for Monday and Tuesday, along with federal government offices and the entire Amtrak rail network on the eastern seaboard.
New York, Boston and Washington DC were effectively shut for business and -- with just eight days to go until polling day -- the US presidential election campaign was severely disrupted.
Streets leading up to Atlantic City's famed ocean-front boardwalk were flooded, and mostly deserted as the city braced for high tide. In nearby Ocean City, a section of promenade was smashed and fell into the storm surge.
PRIORITY TO SAVE LIVES: OBAMA
Obama cancelled an appearance in the swing state of Florida, returning to the White House to steer the relief effort.
"The election will take care of itself next week," Obama said. "Right now, our number one priority is to make sure that we are saving lives... and that we respond as quickly as possible to get the economy back on track."
Both the Democrat incumbent and his Republican rival Mitt Romney were keen to display resolute leadership in the face of the storm, given the memory of Hurricane Katrina in 2005. Romney also cancelled some appearances.
Former president George W. Bush was widely seen as having bungled the handling of Katrina, which devastated New Orleans. The failure of authorities in the ensuing emergency response tainted the rest of his presidency.
Although Sandy lacked the sheer force of Katrina, it has a broader front and will combine with cold weather bearing down from Canada to wreak havoc in a climatic confluence of events dubbed a "Perfect Storm".
Obama has already signed emergency declarations to free up federal disaster funds for New York state, Massachusetts, Connecticut, Maryland, the District of Columbia, New Jersey, Pennsylvania and Rhode Island.
"There will undoubtedly be some deaths," Maryland governor Martin O'Malley told reporters, citing the intensity of the storm and likely floods caused by the tidal surge and high waves.
A Maryland motorist died in a road accident as the winds and rain lashed the state but officials would not directly link it to the foul weather.
Sea levels in New York Harbor and the Long Island Sound rose by nine feet and experts said that if, as feared, they swell by 11 feet (three meters) -- thanks to high tides -- they could cause catastrophic flooding.
Around 1,900 members of the National Guard have been activated and around 60,000 more are on standby, the Pentagon said, with 140 helicopters being made available in anticipation of rescue and relief efforts.
