Millions of people in the eastern US awoke on Tuesday to flooded homes, fallen trees and widespread power outages caused by the giant storm Sandy, which swamped the subway system and submerged streets in Manhattan.

At least 15 people were reported killed in the US by Sandy, one of the biggest storms to ever hit the country, which dropped just below hurricane status before making landfall on Monday night in New Jersey.

More than 1 million people in a dozen states were under orders to evacuate as the massive system plowed westward.

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

The storm interrupted the presidential campaign a week before Election Day and closed U.S. financial markets for two days.

Sandy, which was especially imposing because of its wide-ranging winds, brought a record storm 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 course under the city, raising concerns that the world's financial capital could be hobbled for days.

"Hitting at high tide, the strongest surge and the strongest winds all hit at the worst possible time," said Jeffrey Tongue, a 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," he added.

Large sections of New York City were 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 subway, bus and commuter train system, MTA spokesman Aaron Donovan said.

50-plus homes burn

The unprecedented flooding hampered efforts to fight a massive fire that destroyed more than 50 homes in Breezy Point, a private beach community on the Rockaway barrier island in the New York City borough of Queens, the Fire Department of New York said.

Two people in New York City reportedly died in the storm - 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 two others were reported killed on suburban Long Island.

A motor vehicle death in Massachusetts was blamed in part on the bad weather. Two other people 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.

More than 7 million people in several states were without electricity due to the storm, which crashed ashore late on Monday near the gambling resort of Atlantic City, New Jersey.

The storm was plowing westward over south-central Pennsylvania, still packing near hurricane-force winds as strong as 65 miles per hour (105 km per hour), the National Weather Service said.

Wind gusts, rain and flooding were likely to extend well into Tuesday, but without the storm's earlier devastating power, said AccuWeather meteorologist Jim Dickey.

"Overall, the worst has past," Dickey said.

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 Mountains inland. – Reuters