Sandy, one of the biggest storms ever to hit the US, battered the nation's eastern seaboard on Tuesday, swamping New York City streets with record levels of floodwater, blacking out power to millions of people and bringing transportation to a halt through much of the region.

At least 13 people were reported killed in the United States by Sandy, which dropped just below hurricane status before going ashore in New Jersey on Monday, according to officials and media reports. More than 1 million people across a dozen states were under orders to evacuate as the massive system continued to plow westward.

One disaster forecasting company predicted economic losses could ultimately reach $20 billion, only half insured.

The storm also slowed the presidential campaign at a key time ahead of next week's vote and closed U.S. markets for two days.

Sandy, which was especially imposing because of its wide-raging winds, brought a record surge of almost 14 feet (4.2 meters) to downtown Manhattan, well above the previous record of 10 feet (3 meters) during Hurricane Donna in 1960, the National Weather Service said.

Water poured into the subway system and tunnels that run under the rivers around Manhattan, raising concerns that the world's financial capital could be hobbled for days to come.

"Hitting at high tide, the strongest surge and the strongest winds all hit at the worst possible time," said Jeffrey Tongue, meteorologist for the weather service in Brookhaven, New York.

Hurricane-force winds as high as 90 miles per hour (145 kph) were recorded, he said.

"Hopefully it's a once-in-a-lifetime storm," Tongue said.

Large sections of New York City were in darkness without power and transportation in the metropolitan area was at a standstill.

"In 108 years our employees have never faced a challenge like the one that confronts us now," Metropolitan Transportation Authority Chairman Joseph Lhota said in a statement.

It could take anywhere from 14 hours to four days to get the water out of the flooded subway tunnels, the MTA said.

"The damage has been geographically very widespread throughout the entire subway, bus, LIRR (Long Island Railroad) and Metro North system, MTA spokesman Aaron Donovan said.

50-plus homes burn

The unprecedented flooding was hampering efforts to fight a massive fire in one of the city's barrier island neighborhoods, Breezy Point in the borough Queens, the New York Fire Department said. More than 170 firefighters battled a fire that destroyed more than 50 homes.

Two people were reported dead in New York City - a man in a house hit by a tree and a woman who stepped into an electrified puddle of water. Two other people were killed in suburban Westchester County, north of New York City, and a motor vehicle death in Massachusetts was blamed in part on the bad weather.

Two others were killed in Maryland in storm-related incidents, state authorities said, and deaths also were reported in Connecticut, New Jersey, Pennsylvania and West Virginia, CNN said.

Toronto police also recorded one death - a woman hit by flying debris.

Some 6.8 million people in several states were left without electrical power by the storm, which crashed ashore late on Monday near the gambling resort of Atlantic City, New Jersey.

In New Jersey, Exelon Corp declared an alert around its Oyster Creek nuclear power plant because of rising waters, the U.S. Nuclear Regulatory Commission said. Officials said if waters rose further, they might be forced to use emergency water supplies to cool spent uranium fuel rods.

An alert-level incident, the second-lowest of four action levels, means there's a "potential substantial degradation in the level of safety" at a reactor.

The storm's wind field stretched from South Carolina north to the Canadian border and from West Virginia to a point in the Atlantic Ocean halfway to Bermuda, easily one of the largest ever seen, the National Hurricane Center said.

Heavy snow fell in higher elevations of the Appalachian Mountain inland, and the population centers of Baltimore, Philadelphia and Washington, D.C., were in the slow-moving storm's path.

In New York, a crane partially collapsed and dangled from a 90-story luxury apartment building under construction in midtown Manhattan, and authorities evacuated residents in the area out of fear that high winds would bring the entire rig down.

Much of the city was deserted, as its subways, buses, commuter trains, bridges and airports were closed.

Neighborhoods along the East and Hudson rivers were underwater, as were low-lying streets near Ground Zero, where the World Trade Center once stood.

Power and back-up generators failed at New York University Hospital, forcing patients to be moved elsewhere for care.

In lower Manhattan, firefighters used inflatable orange boats to rescue utility workers stranded for three hours by rising floodwaters inside a power substation.

One of the Con Ed workers pulled from the floodwater, Angelo Amato, said he was part of a crew who had offered to work through the storm.

"This is what happens when you volunteer," he said.

Markets, campaign impacted

Trees were downed across the region, falling debris closed a major bridge in Boston and floodwater and gusts of wind buffeted coastal towns such as Fairfield, Connecticut, home to many commuters into New York City.

With eight days to go before the election, President Barack Obama and Republican challenger Mitt Romney canceled scheduled campaign events and acted cautiously to avoid coming across as overtly political while millions of people are imperiled.

U.S. stock markets were set to be closed on Tuesday. They closed on Monday for the first time since the attacks of Sept. 11, 2001.

The federal government in Washington was closed and schools were shut up and down the East Coast.

NYSE Euronext said there had been no damage to the New York Stock Exchange headquarters that could impair trading floor operations but it was making contingency plans in case of such damage.

Sandy killed 66 people in the Caribbean last week before pounding U.S. coastal areas. – Reuters