Millions of Americans hunkered down on Christmas Day to ride out the freezing storm that has killed at least 24 people and is expected to claim more.
Residents have been trapped inside their homes with heaping snow drifts reaching up to 43 inches and thousands of families and businesses are without power.
The scope of the storm has been nearly unprecedented, stretching from the Great Lakes near Canada to the Rio Grande along the border with Mexico.
About 60 per cent of the US population faced some sort of winter weather advisory or warning, and temperatures plummeted drastically below normal from east of the Rocky Mountains to the Appalachians, the National Weather Service said.
Some 1,346 domestic and international flights were cancelled as of early Christmas Day, according to the tracking site FlightAware.
Forecasters said a bomb cyclone, when atmospheric pressure drops very quickly in a strong storm, had developed near the Great Lakes, stirring up blizzard conditions, including heavy winds and snow.
Hurricane-force winds and snow caused whiteout conditions in Buffalo, while New York governor Kathy Hochul said almost every fire appliance in the city was stranded on Saturday - and shutting down the airport until Monday, according to officials.
The National Weather Service said the snow total at the Buffalo Niagara International Airport stood at 43 inches at 7am on Sunday.
Two people died in their suburban home in Cheektowaga, New York, when emergency crews could not reach them in time to treat their medical conditions, and another died in Buffalo.
Four more deaths were confirmed overnight, bringing the total to seven in Erie County, where county executive Mark Poloncarz warned there may be more dead.
“Some were found in cars, some were found on the street in snowbanks,” he said. “We know there are people who have been stuck in cars for more than two days.”
The storm knocked out power in communities from Maine to Seattle. But heat and lights were steadily being restored across the US.
According to poweroutage.us, fewer than 300,000 customers were without power at 8am on Sunday - down from a peak of 1.7 million.
Storm-related deaths were reported in recent days all over the country including seven in Erie County, New York; 10 dead in multiple crashes in Ohio and a pileup involving some 50 vehicles.
In Florida, the thermometer plunged below freezing for the first time in almost five years at Tampa International Airport, and hit 6.1C in West Palm Beach, according to the National Weather Service.
The temperature drop was conducive to iguanas falling out of trees since the cold-blooded reptiles typically become immobilised in unusually cold weather.
