Sandy began battering the US East Coast yesterday with fierce winds and driving rain, as the monster storm shut down transportation, shuttered businesses and sent thousands scrambling for higher ground hours before the worst was due to strike.

About 50 million people from the Mid-Atlantic to Canada were in the path of the nearly 1,600-kilometer-wide storm, which forecasters said could be the largest to hit the mainland in US history. It was expected to topple trees, damage buildings, cause power outages and trigger heavy flooding.

State governors warned of the acute danger from the winds and torrential rains. "There will undoubtedly be some deaths that are caused by the intensity of this storm, by the floods, by the tidal surge, by the waves. The more responsibly citizens act, the fewer people will die," Maryland Governor Martin O'Malley told reporters.

The US stock market suffered its first weather-related closure in 27 years and many schools and businesses were closed in Washington, Baltimore, Philadelphia and New York.

While the center of the storm was not expected to make landfall until last night near Atlantic City, New Jersey, it was already creating dangerous conditions and forcing rescue workers into action.

The US National Hurricane Center said the Category 1 storm had strengthened as it turned toward the coast and was moving at 30 km per hour. It was expected to bring a "life-threatening storm surge," coastal hurricane winds and heavy snow in the Appalachian Mountains, the center said. Forecasters said Sandy was a rare, hybrid "superstorm" created by an Arctic jet stream wrapping itself around a tropical storm.

Nine US states have declared a state of emergency. Sandy killed 66 in the Caribbean last week before pounding US coastal areas as it moved north. While Sandy does not pack the punch of Hurricane Katrina, which devastated New Orleans in 2005, it could become more potent as it approaches the US coast.

Winds were at a maximum of 150kph, the center said in its 11am report, up from 120kph nine hours earlier. It said tropical storm-force winds reached as far as 780km from the center.

Several feet of water flooded streets in Rehoboth Beach, Delaware, which could be right in the target zone of the storm.

Local residents said police knocked on doors on Sunday, reminding everyone of a mandatory evacuation. While the police took names, they allowed residents to stay at their own risk.

"If power goes that's a problem," said John Brunhammer, 40, a recruiter from Lewes, Delaware, who had come to see the waves crashing up to the dune line at Rehoboth Beach. "This area isn't known for prompt utility service."

New York and other cities and towns closed transit systems and ordered mass evacuations from low-lying areas ahead of a storm surge that could reach as high as 3.4 meters.

By early yesterday, water was already topping the seawall in Manhattan's Battery Park City, one of the areas evacuated by Mayor Michael Bloomberg.

All US stock markets were closing yesterday and possibly today, the operator of the New York Stock Exchange said late on Sunday, reversing an earlier plan that would have kept electronic trading going. The United Nations, Broadway theaters and New Jersey casinos were closing, and more than two-thirds of the East Coast's oil refining capacity was shutting down.

Officials ordered people in coastal towns and low-lying areas to evacuate, telling them they would put emergency workers' lives at risk if they stayed.

Worried residents in the hurricane's path packed stores, searching for generators, flashlights, batteries, food and other supplies in anticipation of power outages. Nearly 384,000 residential properties valued at US$88 billion were at reisk for damage.