The mayor of New York has ordered the mandatory evacuation of 375,000 people ahead of Hurricane Sandy.
Michael Bloomberg said 72 evacuation centres had been set up around the city in schools and community centres.
Subway, bus and train services will be suspended from 7pm local time and hundreds of flights into the city's airports have been rerouted or cancelled.
The New York Stock Exchange will close its trading floor on Monday, but trading will continue electronically.
"This is a serious and dangerous storm," Bloomberg said. "If you don't evacuate you are not just putting your own life in danger, you are also endangering the lives of the first responders who may have to come in and rescue you."
The hurricane is expected to start hitting the area on Sunday night, with the worst weather following on Monday.
All of the city's public schools have been closed, and the evacuation zone includes parts of Coney Island, Manhattan Beach and other areas along the east river in Brooklyn.
Stretches of the Lower East Side, Staten Island and Manhattan are also included.
Hurricane Sandy is heading north from the Caribbean - where it has killed 65 people - to threaten the eastern US with sheets of rain, high winds and heavy snow.
The majority of the deaths have happened in Haiti and the area around the capital Port-au-Prince, which holds most of the 370,000 Haitians who are still living in flimsy shelters as a result of the devastating 2010 earthquake.
Officials said 51 people have died there, though the number is expected to rise.
"This is a disaster of major proportions," Prime Minister Laurent Lamothe said.
The hurricane is expected to affect up to 60 million people in the US when it meets a winter storm and a cold front, plus high tides from a full moon.
Experts said the rare hybrid storm that results will cause havoc over 800 miles (1,300km) from the East Coast to the Great Lakes.
Tens of thousands of people along the coast in Delaware, New Jersey, Connecticut and other threatened areas were under orders to clear out because of the danger of as much as a foot of rain, winds of 80 mph and a tidal surge of up to 8ft.
Sandy was at Category One strength, packing 75mph (120kph) winds, about 260m (418km) southeast of Cape Hatteras, North Carolina, and moving northeast at 10mph (16kph) as of 8am (1200 GMT) on Sunday, according to the National Hurricane Centre in Miami.
It was about 395m (635km) south of New York City.
Officials warned that the rain could saturate the ground, causing trees to topple onto power lines and cause blackouts that could last for several days.
Parts of West Virginia, Virginia, Kentucky and North Carolina could get 2ft or more of snow in places.
US rail provider Amtrak began cancelling train service Saturday night in parts of the East Coast, including between Washington and New York.
Airlines were moving planes out of airports to avoid damage, and added Sunday flights out of New York and Washington in preparation for flight cancellations on Monday.
The Virginia National Guard had been authorised to call up 500 troops for debris removal and road-clearing, while homeowners stacked sandbags at their front doors in coastal towns.
