Hurricane Sandy is threatening 50 million people on America's heavily-populated East Coast, with forecasters warning that New York could bear the brunt of the one-of-a-kind superstorm.
Federal Emergency Management Administrator Craig Fugate warned the "time for preparing and talking is about over" as Sandy makes 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, and states of emergency have been declared from North Carolina to Connecticut.
Airlines cancelled more than 7,600 flights and Amtrak has suspended passenger train services across the north-east.
New York and Philadelphia moved to shut down their subways, buses and commuter trains on Sunday night and announced that schools would be closed on Monday. Boston, Washington and Baltimore also shut down schools.
As rain from the leading edges of the monster hurricane began to fall over the north-east, 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 the 34-year history of legalised gambling there.
Authorities have 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.
The National Hurricane Centre said the Category 1 hurricane had top sustained winds of 75mph, with higher gusts. 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 on Monday or early Tuesday, most likely in New Jersey, colliding with a wintry storm moving in from the west and cold air streaming down 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 outwards from the storm's centre. It could also dump up to 2ft of snow in Kentucky, North Carolina and West Virginia.