It is bitterly cold across eastern Canada and the north-eastern United States, with temperatures in some cities reaching as low as -40C.
By Lee Carter
BBC correspondent in Toronto
Icy winds are adding a severe wind chill factor in some regions.
Although eastern Canada is used to cold weather, the latest extreme temperatures are proving potentially dangerous for some.
In the country's largest city, Toronto, homeless shelters are packed with people trying to escape the cold.
City officials say there could still be up to 1,000 people without shelter out on the streets, where frigid temperatures have been exacerbated by heavy blowing snow.
The coldest temperatures can be found in Canada's maritime provinces.
Schools are closed on Prince Edward Island and in New Brunswick, where health officials are warning that skin can freeze within 10 minutes.
Those who were hardy enough to venture out had to wrap even more than they normally would at this time of the year.
Homeless people are particularly vulnerable to the freezing weather
"I got a lot of stuff on me," said one muffled person in the street.
"I'm just like a bear. I can barely move."
"I don't think you ever get used to this kind of weather," said another.
But another appeared unperturbed by the extremes of weather.
"It's cold, you dress accordingly and deal with it."
On Wednesday, there were power cuts in parts of Montreal and all across the region.
Electricity utilities say they fear the cold temperatures could boost power consumption to breaking point.
The frigid Arctic air also stretches across the American north-east, affecting New England and as far south as New York City, where once again protecting the homeless has become a priority.
The deep freeze is expected to last several days.