Barack Obama has warned Americans to take Hurricane Sandy seriously as authorities started shutting down the eastern seaboard ahead of its arrival.
Several states have declared emergencies, with tens of millions of people affected as schools are closed and transport services suspended.
Experts fear Sandy may become a super-storm when it makes landfall later.
Some election rallies have been called off, with Mr Obama warning affected citizens to take precautions.
International travel has been badly affected. Air France, British Airways and Virgin Atlantic grounded Monday's transatlantic flights to and from East Coast cities, including New York, Baltimore, Newark, Washington DC, Boston and Philadelphia.
Sandy has already killed 60 people as it swept through the Caribbean during the past week.
At 05:00 EDT (09:00 GMT), the storm was swirling about 385 miles (615km) south-east of New York City, according to the National Hurricane Center.
Worryingly, forecasters said its maximum sustained winds had increased to 85mph (140km/h) from 75mph recorded hours earlier.
Hurricane Sandy, dubbed "Frankenstorm", is expected to bring a "life-threatening" surge flood to the mid-Atlantic coast, including Long Island Sound and New York Harbour.