Some 200 million Americans are under a weather advisory as a massive winter storm tightens its icy grip on the country ahead of the holiday weekend.
More than 1.5 million people lost power and thousands of flights were cancelled on Friday.
So far at least 12 deaths linked to the storm have been confirmed across the country.
A bomb cyclone, when atmospheric pressure plummets, brought blizzard-like conditions to the Great Lakes.
In Canada, Ontario and Quebec were bearing the brunt of the storm, which is causing power cuts for hundreds of thousands of households.
In the US, the vast storm spans 2,000 miles (3,200km) from Texas to Maine, and the National Weather Service (NWS) said its Friday map “depicts one of the greatest extents of winter weather warnings and advisories ever”.
Temperatures in Elk Park, Montana, dropped to -50F (-45C).
Heavy snowfall was forecast in areas of Pennsylvania and Michigan. Buffalo, New York, was expecting at least 35in (89cm).
Even the usually milder southern states of Louisiana, Alabama, Florida and Georgia were subject to hard-freeze warnings.
A number of the storm-related fatalities have involved road traffic accidents, including a 50-car pile-up in Ohio that left at least one person dead.
More than 8,000 flights were cancelled on Friday, reported tracking site FlightAware, wreaking yet more travel chaos as travellers battle to make it home for Christmas.
The latest figure for customers without electricity across the US by Friday evening was 1.2 million, according to PowerOutage.us.
Utilities throughout the Tennessee Valley were implementing rolling blackouts to save power.
The cold has matched decades-old temperature records across the US:
- Denver, Colorado, dropped to -24F on Thursday, its lowest point since the 1990s
- Wichita, Kansas, recorded its coldest wind chill (-32F) since 2000
- Nashville, Tennessee, saw its temperatures plunge to below zero for the first time in 26 years
- Casper, Wyoming, set a new record low on Tuesday of -42F
New York, West Virginia, Kentucky, Georgia, North Carolina and Oklahoma have declared states of emergency, while Wisconsin declared an “energy emergency”.
In South Dakota, Native American tribe members were reportedly burning clothes for warmth after running out of fuel and being trapped by massive snow drifts.
“We’re fighting a losing battle,” says Oglala Sioux Tribe President Frank Star Comes Out told the BBC. He said it is unclear how many of the tribe’s 46,000 members are trapped across the 4,200 sq mile region.
Machinery is failing as diesel fuel turns to gel in the freezing cold. Some rescuers are using horses and sleds, or walking.
Anna Halverson, who represents the Pass Creek District on the Pine Ridge Reservation, told the Darsha Dodge Rapid City Journal: “We’re in a really extreme emergency down here.”
“We have drifts as high as some houses that stretch 60, 70 yards at a time.”
She said one family had run out of infant formula, food and fuel and spent four days trapped inside before walking eight miles to get help because their baby was starving.
“I’ve seen across the reservation some members were burning clothes in their wood stove because they couldn’t get access to wood,” Ms Halverson said.
South Dakota Governor Kristi Noem has activated the state’s National Guard to haul firewood from a nearby national forest to the Rosebud Sioux Tribe and the Oglala Sioux Tribe.
