Hurricane Sandy is bearing down on the US East Coast, threatening serious flooding and power cuts that could affect 50 million people.
Hundreds of thousands of residents have been ordered to evacuate New York City and New Jersey, reports the BBC.
Public transport has been suspended in cities up the eastern seaboard and thousands of flights grounded.
Forecasters fear Sandy will become a super-storm when it collides with cold weather fronts from the west and north.
The category one hurricane coincides with a full moon, which is bringing higher tides.
At the White House, President Barack Obama warned Americans in harm’s way to follow emergency instructions.
“Do not delay, don’t pause, don’t question the instructions that are being given,” said Obama, who has cancelled campaign events, eight days before the US elections.
“This is going to be a big storm, it’s going to be a difficult storm.”
The president has signed nine emergency declarations: New York, New Jersey, Massachusetts, Connecticut, Rhode Island, Delaware, Pennsylvania, Maryland and District of Columbia.
The storm threatens to devastate an 800-mile (1,290-km) swathe of the US, from the Atlantic Ocean to the Great Lakes in the Mid-West.
Up to 3ft (91cm) of snow is expected to fall on the Appalachian mountains in West Virginia, Virginia and Kentucky.
The storm has already killed 69 people – 52 of them in Haiti – after sweeping through the Caribbean in the past week.
At 14:00 EDT (18:00 GMT), Sandy was churning about 170 miles south-east of New York City, the National Hurricane Center (NHC) said.
The storm had strengthened from the morning, packing maximum sustained winds clocked at 90mph with higher gusts.
Hurricane force winds extended for 175 miles and tropical storm force winds for 485 miles, the NHC added.
The eye of the weather system, which has been dubbed Frankenstorm, is expected to make landfall just south of the New Jersey coast by early evening, the NHC said.
Forecasters say the vast hurricane could linger over as many as 12 states for 24-36 hours, bringing up to 10in of rain, 24in of snow, extreme storm surges and power cuts.
President Obama cancelled a planned rally in Florida with former President Bill Clinton on Monday and an event for Tuesday in Wisconsin, far from the storm.