NEW YORK (UPDATE) - Monster storm Sandy swept a wall of churning sea water and driving rain onto the eastern United States on Monday, flooding the heart of downtown New York and leaving at least 13 dead.
Seawater coursed between the iconic skyscrapers of New York's financial district in lower Manhattan, flooding subways and road tunnels and shorting out the power grid, plunging hundreds of thousands into darkness.
Further south, vast swathes of the eastern seaboard found themselves under water and on inland mountains Sandy's rain-heavy clouds had merged with a cold weather front to dump tons of snow on higher ground.
The catastrophe completely overshadowed the US election race, forcing a halt to campaigning just eight days before Americans are due to go to the polls to choose between President Barack Obama and challenger Mitt Romney.
Hurricane Sandy had killed 67 people as it tore through the Caribbean, and reports of more deaths began to arrive after it made landfall at 8:00 pm (0000 GMT) in New Jersey and began to wreak havoc in the United States.
Local officials in New York, New Jersey, Pennsylvania, Maryland, West Virginia and North Carolina reported 13 dead in storm related incidents, and Toronto police said a Canadian woman was killed by flying debris.
Authorities warned the threat to life and property was "unprecedented" and ordered hundreds of thousands of residents in areas from New England to North Carolina to evacuate their homes and seek shelter.
The National Hurricane Center said wind speeds inside Sandy dropped as the storm became a post-tropical cyclone, but remained hurricane-force at 75 miles per hour (120 kmph) after making landfall near casino resort Atlantic City.
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.
A nuclear power plant in New Jersey declared an alert as waters rose.
The Oyster Creek nuclear power plant, just north of Atlantic City, was already on a scheduled outage as Sandy made landfall, and the industry regulator said there was no immediate danger.
"Water level is rising in the intake structure due to a combination of a rising tide, wind direction and storm surge," the Nuclear Regulatory Commission said, adding that inspectors were working with the firm to ensure safety.
"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 coast to 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," Obama said.
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.
"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 Democratic incumbent and his Republican rival Romney were keen to display resolute leadership in the face of the storm, given the memory of Hurricane Katrina in 2005. Romney also canceled 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.
Obama has 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.
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