North America’s brutal cold snap is headed to grip east, ushering in the coldest temperatures not seen in two decades, warn forecasters.
From Montana to Maryland, about half of the US population has been placed under a wind chill warning or advisory.
In Canada, the province of Ontario is facing temperatures of -40C (-40F) with wind chill.
Thousands of flights have been grounded, and residents told their skin could freeze if they go outside.
People on the US north-east coast were warned to prepare themselves for the cold front sweeping in on Tuesday from the Midwest.
Temperatures were set to plummet overnight in New York and Washington DC by as much as 45 degrees, from unseasonably clement highs a day earlier.
New York Governor Andrew Cuomo announced that parts of major highways would be closed in preparation for the extreme weather, which could see the mercury plummet to -26C (15F) overnight with wind chill.
The polar blast was threatening crops and livestock across the American farm belt, even in the usually temperate Deep South.
The weather has been blamed for at least 16 deaths in recent days.
Meteorologists said some 187 million people in all would be able to feel the effects of the cold snap by Tuesday.
It has been widely blamed on a shift in the weather pattern known as the “polar vortex”.
In Comertown, Montana, on Monday the temperature sank to -53C (-63F) with wind chill.
