A stream of bitterly cold weather is sweeping through parts of the United States, disrupting transport, forcing schools to close and prompting warnings to stock up on food and stay indoors.
Already hit by a winter storm, parts of the United States and Canada are braced for potentially record-breaking low temperatures as a huge whirlpool of frigid air known as a polar vortex swirls over the region.
Areas of Canada and the north-eastern US have already been blanketed with up to 60cm of snow. The storm and the deep cold have been blamed for 16 deaths in recent days.
More than 3000 flights were cancelled on Monday, in addition to thousands grounded over the weekend.
The blast of Arctic air gripping the north and central US is sending temperatures plummeting, and forecasters say it could feel as cold as -51°C with the effect of wind chill.
Temperatures were between 11°C and 22°C below average in parts of Montana, North and South Dakota, Minnesota, Iowa, Wisconsin, Michigan and Nebraska, Reuters reported, citing the National Weather Service.
In North Dakota, temperatures are forecast to be so low that just 10 minutes out in the open could freeze someone's eyeballs.
The polar blast was moving eastwards on Tuesday where temperatures have plummeted in New York, while Washington DC and parts of Canada are expecting the coldest weather in 20 years.
Many children will stay at home as schools in parts of the US have been forced to close. A driving ban was put in place in some areas and the Governor of Illinois declared a state of emergency.
Environment Canada's David Phillips told the BBC the rapid temperature drop expected - about 24°C in 24 hours in cities such as Toronto - means residents could be driving or walking on roads that are "like a rink of ice".
In Thunder Bay, Ontario, the temperature on Monday morning was -33°C, and temperatures in eastern Canada were expected to drop quickly throughout Monday. Freezing rain caused long airport delays in Toronto and Ottawa.
Link to global warming
A climate researcher says the cause of the bitter chill gripping North America could be traced to global warming.
Dim Coumou, a senior scientist at the Potsdam Institute for Climate Impact Research in Germany, says Arctic air is normally penned in by a powerful circular wind called the polar vortex.
Mr Coumou says the rapid warming of the Arctic in recent years, where temperatures are rising at about twice the global average, is blurring the difference between polar temperatures and those in middle latitudes, thus causing the vortex to weaken, AFP reports.
When it weakens, he says, the air starts heading southwards, bringing exceptional snow and chill to middle latitudes.