The coldest wind chill ever has been recorded in the US as temperatures plunged to -77C.
Icy gusts ripped through Mount Washington in New Hampshire on Friday dragging the air down to the record low, according to the National Weather Service (NWS).
More than 100 million people living in the US and Canada have been hit by the Arctic blast - with authorities warning frostbite could latch on within a matter of minutes.
The "once-in-a-generation" cold snap has lead officials to urge Americans to limit time outdoors between Friday and Saturday.
At 8pm last night (1am GMT), the actual temperature on Mt Washington plummeted to -46F - the coldest ever recorded at the same location.
The New England state of Maine, and Quebec in Canada, are set for record low wind chills - the likes of which were last seen in the 1980s.
While power companies expected historic levels of energy use this morning, residents of Austin, Texas, faced an icy start after they lost power - and in many cases heat.
Communities have been forced to close schools and open warming centres, including in New York City where homeless residents can seek shelter and warmth from the -23C air.
While New England began shivering and closed school temperatures finally started to moderate Friday and bring some relief in Austin.
At any given time, about 30 per cent of customers in the nation's 11th largest city were without electricity since the ice storm swept into Texas late on Monday.
City officials said Friday that significant progress was finally being made as frozen equipment and roads thawed. About 117,000 customers still lacked power, according to Austin Energy, the city's utility. That's down from a peak of around 170,000 people, nearly a third of all customers.
But frustration was not melting away for residents who still had no assurances or sense of when their power would return.
"I just honestly think they were not prepared for any of this," said Edward Kim, 43, whose home had been without power or heat since Wednesday. He was using a generator to keep his house "on life support," while his wife took her 7-year-old daughter to her office to get a shower.
There have been no reports of deaths from this week's power outages, though the storm and freeze have been blamed for at least 12 traffic fatalities on slick roads in Texas, Arkansas and Oklahoma.
Two fatal crashes occurred in Fort Worth as streets refroze overnight. Lows on Friday night could reach freezing and potentially glaze over the streets again.
Schools closed Friday in Boston and in Manchester, New Hampshire's largest city. "This is simply too cold for students who walk home," read an announcement on the Manchester district's website.
Some ski areas in the two states scaled back operations, eliminating night skiing or reducing lift operations.
In Maine, the National Toboggan Championship pushed Saturday's races back by a day, just two weeks after relocating the competition because a pond wasn't yet frozen due to warm weather.
The irony of delaying competition because of frigid conditions wasn't lost on Holly Anderson, one of the organizers.
"We've done subzero competitions before. But the wind totally changes the environment. It just makes it untenable to be outside," Anderson said.
The system is expected to move out of the region Sunday.
