Hurricane Sandy is threatening 50 million people on America's east coast with forecasters warning that New York could bear the brunt of the one-of-a-kind superstorm.
Federal emergency administrator Craig Fugate warned that the "time for preparing and talking is about over" as Sandy made its way up the Atlantic on a collision course with two other weather systems that could turn it into one of the most fearsome storms on record in the US.
"People need to be acting now," he said.
Forecasters warned the megastorm could wreak havoc over 800 miles from the east coast to the Great Lakes. States of emergency were declared from North Carolina to Connecticut.
Airlines cancelled more than 7,600 flights and Amtrak began suspending passenger train service across the Northeast. New York and Philadelphia moved to shut down their subways, buses and commuter trains last night and announced that schools would be closed today. Boston, Washington and Baltimore also shut down schools.
As rain from the leading edges of the monster hurricane began to fall over the Northeast, tens of thousands of people in coastal areas from Maryland to Connecticut were under orders to clear out.
That included 50,000 in Delaware alone and 30,000 in Atlantic City, New Jersey, where the city's 12 casinos were forced to shut down for only the fourth time in history.
Authorities warned that the biggest US city could get hit with an 11ft wall of water that could swamp parts of lower Manhattan, flood subway tunnels and cripple the network of electrical and communications lines that are vital to the nation's financial centre.
Sandy, a Category 1 hurricane, was about 470 miles south east of New York City and the centre of the storm is expected to be near the mid-Atlantic coast tonight.
It is moving towards the north east at 14mph. Hurricane-force winds extend up to 175 miles from the storm's centre.
Sandy was expected to hook left towards the mid-Atlantic coast and come ashore late today or early tomorrow, most likely in New Jersey, colliding with a wintry storm moving in from the west and cold air streaming from the Arctic.
Forecasters said the monster combination could bring close to a foot of rain, a potentially lethal storm surge and punishing winds extending hundreds of miles outward from the storm's centre. It could also dump snow in Kentucky, North Carolina and West Virginia.