New York City, Boston and other areas in the north-eastern US have shut down, with forecasters warning residents to expect “crippling” amounts of snow.
Winter Storm Juno was expected to dump up to 60cm (24in) of snow near New York City, and in Connecticut, Rhode Island, Massachusetts and New Hampshire.
Meteorologists downgraded their initial forecasts, lifting blizzard warnings in New York City and New Jersey.
Some 60 million people may be affected by the shutdown.
Driving bans for all but emergency vehicles are in place in New York and Boston, with subway systems suspended.
An emergency has been declared in the states of New York, New Jersey, Connecticut, Rhode Island, Massachusetts and New Hampshire.
Meteorologists initially predicted up to 90cm (36in) of snow, but later revised their forecasts.
Parts of eastern Pennsylvania and New Jersey have been spared extreme snow, and at least one winter storm warning in New Jersey has been cancelled.
However, the National Weather Service (NWS) warned that the storm could still bring “crippling snowfall amounts and life-threatening blizzard conditions to much of the north-east”.
In other developments:
6,500 flights in and out of airports along the East Coast have been cancelled
Businesses and schools closed early on Monday
Schools are not expected to reopen before Wednesday at the earliest
Boston is expected to bear the brunt of the storm
The NWS had previously warned that a “potentially historic blizzard” was approaching the north-east.
However, the blizzard appeared less severe than expected on Tuesday morning, with snowfall levels ranging from 2.5cm (1in) in Washington DC to 38cm (15in) at New York State’s Islip airport at 03:00 local time (08:00 GMT).
Meteorologists expect the snow and strong winds to continue throughout Tuesday, before weakening overnight.
