More than 5.5 million people were left without electrical power by the Hurricane Sandy , which crashed ashore late Monday near the gambling resort of Atlantic City, New Jersey. More than one million people across a dozen states were ordered to evacuate.
At least 12 people have reportedly been killed, the first US fatalities from a storm that had already killed more than 60 people in the Caribbean.
Heavy snows threatened mountainous regions inland, and huge population centers of Baltimore, Philadelphia and Washington, D.C. lay in the storm's path.
"We have not seen the kind of flooding problems that certainly could have happened thus far, but we've still got a long ways to go to get through this storm," Washington Mayor Vincent Gray said on local television.
Streets of New York City filled with floodwater, raising fears that the city's subway tunnels could be inundated, and flying debris blew along deserted sidewalks. The city closed down subway, bus and commuter train systems on Sunday night.
In lower Manhattan, firefighters used inflatable orange boats to rescue utility workers trapped 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.
Two people were killed in the New York borough of Queens -- a man in a house hit by a falling tree and a woman who stepped into an electrified puddle of water. Massachusetts police said one man was killed in Peabody in an accident related to the bad weather. Toronto police also recorded one death, a woman hit by flying debris.
Power and back-up generators failed at New York University hospital, and patients were being elsewhere for care.
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, where police cruisers blocked access to the beaches.
"People are definitely not taking this seriously enough," said police officer Tiffany Barrett. "Our worst fear is something like Katrina and we can't get to people."
The storm's wind field stretched from the Canadian border to South Carolina, and from West Virginia to an Atlantic Ocean point about halfway between the United States and Bermuda, easily one of the largest ever seen.
The National Hurricane Center said Sandy came ashore as a "post-tropical cyclone," meaning it still packed hurricane-force winds but lost the characteristics of a tropical storm. It had sustained winds of 80 miles per hour (129 kph), well above the threshold for hurricane intensity.
With eight days to go before the election, President Barack Obama and Republican challenger Mitt Romney canceled scheduled campaign events. Both candidates acted cautiously to avoid coming across as overtly political while millions of people are imperiled.
US stock markets were closed on Monday for the first time since the attacks of September 11, 2001, and were set to remain shut on Tuesday. 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.
One disaster forecasting company predicted economic losses could ultimately reach $20 billion, only half insured.
Governors up and down the East Coast declared states of emergency. Maryland's Martin O'Malley warned there was no question Sandy would kill people in its path.
Sandy made landfall just south of Atlantic City, about 120 miles (190 km) southwest of Manhattan. Casinos in the gambling destination had already shut down.
In New York, officials evacuated neighbors of a 90-story super luxury apartment building under construction after its crane partially collapsed in high winds, prompting fears the entire rig could crash to the ground.
New York electric utility Con Edison said it expected "record-size outages," with 588,000 customers in the city and nearby Westchester County without power. The company is facing both falling trees knocking down power lines from above and flood waters swamping underground systems from below.
While Sandy does not have the intensity of Hurricane Katrina, which devastated New Orleans in 2005, it killed 66 people in the Caribbean last week before pounding US coastal areas as it moved north.
An AccuWeather meteorologist said Sandy "is unfolding as the Northeast's Katrina," and others said Sandy could be the largest storm to hit the mainland in US history.
Off North Carolina, the US Coast Guard rescued 14 of the 16 crew members who abandoned the replica ship HMS Bounty, using helicopters to lift them from life rafts. The Coast Guard later recovered the body of an "unresponsive" 42-year-old woman while continuing to search for the 63-year-old captain of the ship, which sank in 18-foot (5.5 meters) seas.
In New Jersey, Exelon Corp declared an alert around its Oyster Creek nuclear power plant be ause of rising waters, the US Nuclear Regulatory Commission said. Officials said if waters rise further, they may be forced to use emergency water supplies from a fire hose 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.