A behemoth storm packing hurricane-force winds and blizzard conditions has swept through the US north-east, killing at least four people and shutting down a nuclear power station.
The storm dumped more than half a metre of snow on New England and knocked out power to 650,000 homes and businesses.
Three of the deaths blamed on the storm were in Canada and one was in New York.
In southern Ontario, an 80-year-old woman collapsed while shovelling her driveway and two men were killed in car crashes.
In New York, a 74-year-old man died after being struck by a car in Poughkeepsie; the driver said she lost control in the snowy conditions, police said.
Forecasters said wind gusts exceeding 120km/h could cause more widespread power outages and whip the snow into fearsome drifts.
The Pilgrim Nuclear Power Plant in Plymouth, Massachusetts, lost electricity and shut down on Friday night during the storm. Authorities said there was no threat to public safety.
Spokesman Neil Sheehan said the plant had declared an unusual event, which is the lowest level of emergency classification. He said that the reactor shut down without any problems and that back-up generators were powering plant equipment.
More than 70 centimetres of snow had fallen on central Connecticut by early on Saturday, and areas of south-eastern Massachusetts, Rhode Island and New Hampshire notched 0.6 metres or more of snow - with more falling.
Airlines scratched more than 5300 flights throughout Saturday, and New York City's three major airports and Boston's Logan Airport closed.
The wind-whipped snowstorm mercifully arrived at the start of a weekend, which meant fewer cars on the road and extra time for sanitation crews to clear the mess before commuters in the New York-to-Boston region of roughly 25 million people have to go back to work. But it could also mean a weekend cooped up indoors.
The National Weather Service says up to a metre of snow is expected in Boston, threatening the city's 2003 record of 70.1 centimetres. A wind gust of 122km/h was recorded at Logan Airport.
In heavily Catholic Boston, the archdiocese urged parishioners to be prudent about attending Sunday Mass and reminded them that, under church law, the obligation "does not apply when there is grave difficulty in fulfilling this obligation".
Halfway through what had been a mild winter across the north-east, blizzard warnings were posted from parts of New Jersey to Maine. The National Weather Service said Boston could get close to a metre of snow by Saturday evening, while most of Rhode Island could receive more than 60 centimetres, most of it falling overnight Friday into Saturday.
Connecticut was bracing for 60 centimetres, and New York City was expecting as much as 36 centimetres.
Early snowfall was blamed for a 19-car pile-up in Cumberland, Maine, that caused minor injuries.
In New York, hundreds of cars began getting stuck on the Long Island Expressway on Friday afternoon at the beginning of the snowstorm and dozens of motorists remained disabled early on Saturday as police worked to free them.
About 650,000 customers in the north-east lost power during the height of the snowstorm, most of them in Massachusetts and Rhode Island.
Flooding was expected along coastal areas still recovering from Superstorm Sandy, which hit New York and New Jersey the hardest and is considered Jersey's worst natural disaster.
A group of stranded European business travellers, had to wait out the storm in a hotel restaurant on Friday night in downtown Boston, where snow blew outside and drifted several centimetres deep on the footpaths.
The six Santander bank employees found their flights back to Spain cancelled, and they gave up on seeing the city or having dinner out.
"We are not believing it," said Tommaso Memeghini, 29, an Italian who lives in Barcelona. "We were told it may be the biggest snowstorm in the last 20 years."