Thick snow is blanketing the north-eastern US and eastern Canada as a major storm cuts power to thousands of homes and plays havoc with transport.
Massachusetts, Rhode Island, New York, Connecticut and Maine are all on an emergency footing, with millions of residents being warned to stay indoors.
Massachusetts Governor Deval Patrick has temporarily banned all non-essential traffic on the state’s roads.
Meteorologists say the storm could be New England’s worst for decades.
Airlines cancelled more than 4,300 flights – including all those to and from the three major airports in New York City – and the train operator Amtrak has suspended nearly all services north of the city.
People have been warned to stay off the roads, and stock up on food and other supplies as the storm affects 25 million people in the region.
More than 330,000 power cuts have been reported in Massachusetts, Rhode Island and Connecticut.
A nuclear power station in Massachusetts also lost power and was forced to shut down. Back-up generators are operating equipment and there is no threat to the public, officials said.
Canadians on the Atlantic Coast are also bracing for blizzards after heavy snow fell on Ontario.
New Brunswick, Nova Scotia and Newfoundland are under blizzard or storm watches.
Ontario has already seen 200 vehicle accidents, the CBC reported. At least three people have been killed.
One US man in his 70s also died when he lost control of his vehicle in Poughkeepsie, New York.
‘Stay home’
Blizzard warnings are in effect for much of the coastal section of the north-eastern US, from Newark to southern Maine.
Forecasters said the storm could dump as much as three feet (90cm) of snow in some places as it hammered swathes of territory, with winds of up to 75mph (120km/h) expected to create deep drifts.
Police in New York say hundreds of cars are stuck on the Long Island Expressway, with officers trying to help the drivers to safety.
Parts of Massachusetts were already under a foot of snow by Friday night, with more expected over the weekend.
“This is a storm of major proportions,” warned Boston Mayor Thomas Menino. “Stay off the roads. Stay home.”
Connecticut Governor Dannel Malloy said: “People need to take this storm seriously. Please stay home once the weather gets bad except in the case of real emergency.”
In New York City, which is expecting a 12in dousing, Mayor Michael Bloomberg said snow ploughs and 250,000 tonnes of salt were being put on standby.
The storm has also disrupted New York Fashion Week, which is held under a big tent. Organisers say they will bring in extra crews to help with snow removal and add an extra layer of tenting to the venue.
Some neighbourhoods in the city are still recovering from Sandy, an October storm that brought record flooding. Many of those areas face a renewed risk of storm surge and flooding from the winter storm.
Fuel shortages were being reported from Connecticut to New York City as motorists queued at petrol stations to fill up vehicles, generators and snow blowers.
Mayor Bloomberg urged residents not to panic-buy fuel.
The National Weather Service had earlier said the combination of two weather systems from the polar and sub-tropical jet streams would produce a “potentially historic” storm.