Forecasters say the coldest wind chill ever has been recorded in the continental US as an Arctic cold snap freezes a swathe of North America.
The National Weather Service (NWS) said the icy gusts on Mount Washington in New Hampshire on Friday produced a wind chill of -108F (-77C).
Nearly 100 million people across the north-eastern US and Canada are shivering in the frigid blast.
Authorities warned frostbite could strike in less than 10 minutes.
Residents from Manitoba to Maine are being urged to limit their time outdoors until Saturday in the “once-in-a-generation” cold snap.
The NWS said the actual temperature on the summit of Mount Washington at 20:00 on Friday (01:00 GMT Saturday) was down to -46F – the coldest ever recorded there.
The combined effect of wind and cold is also expected to bring some of the lowest wind chill temperatures since the 1980s in the New England state of Maine, as well as in Quebec and parts of eastern Canada.
Power companies were expecting historic levels of energy consumption into Saturday morning during the coldest period.
Boston is under a cold emergency. Public schools have been closed in the city, as well as in nearby Worcester and in Buffalo, New York.
New York City – which could see wind chills as low as -10F (-23C) – has enacted an emergency designation that allows the homeless to go to any shelter to seek warmth.
Nor were the Midwestern states of Michigan, Wisconsin, Indiana, Illinois and Ohio spared by the freezing temperatures.
Parts of Canada were expecting temperatures as low as -58F. An extreme cold advisory issued by Environment Canada on Friday morning blanketed the Maritimes, most of Quebec and all of Ontario, spilling into Manitoba.
In Toronto, the wind chill plunged the temperature to -29C (-20F) on Friday.
Forecasters predict temperatures will rebound by the end of the weekend.
The drop in temperatures is attributed to a powerful Arctic front that stretches from the Canadian maritime provinces to the core of the US.
The brutal winter weather follows this week’s deadly ice storm in parts of Texas, where temperatures have begun to climb above freezing, and ice was expected to melt on Friday.
At least 11 people have died in the bad weather in the US south since Monday. There were eight fatalities in Texas, two in Oklahoma and one in Arkansas.
More than 250,000 people were still without power as of Friday night in Texas, Arkansas, Mississippi, Tennessee and New York, according to poweroutage.us.