A brutal blast of Arctic air has settled over eastern North America, bringing dangerously low temperatures not seen in decades.
About half of the US population has been placed under a wind chill warning or cold weather advisory.
In Toronto, the temperature dropped to -24C (-11F) before dawn on Tuesday.
Air, rail and road travel remain snarled by high, freezing wind, and residents have been warned to stay indoors to avoid frostbite.
Cold air broke records in Chicago on Monday, where the temperature of -16F (-27C) was the lowest ever seen on that date.
It was one of more than 120 daily temperature records broken in cities across the US since the beginning of 2014, many dating back decades.
Sharp temperature drop
The arrival late on Monday of the arctic weather pattern caused temperatures to plummet overnight in New York and Washington DC by as much as 45 degrees in a matter of hours, from unseasonably warm highs a day earlier.
New York Governor Andrew Cuomo closed parts of major highways across his state in preparation for the extreme weather.
Adding to the misery, forecasters say the areas on the eastern shores of the Great Lakes could again be blanketed by snow, as the cold air moved over the water.
In Canada, 4,000 residents of Quebec and 1,000 in Newfoundland were still without power on Tuesday amid the freezing temperatures and snow.
The polar blast was threatening crops and livestock across the American farm belt, even in the usually temperate Deep South. The freeze was expected to reach as far south as Texas and central Florida, the National Weather Service said.
Meteorologists said some 187 million people in all would feel the effects of the cold by Tuesday.
The temperatures have been widely blamed on a shift in the weather pattern known as the "polar vortex".
On Tuesday, the extreme weather caused the cancellation of 2,500 flights, along with widespread road and rail delays.
JetBlue Airways operations, which had been suspended at airports in Boston and around New York City, were returning to normal.
More than 500 passengers on their way to Chicago were stuck overnight in northern Illinois on three Amtrak passenger trains after drifting snow and ice covered the tracks.
And in Indianapolis, Indiana, it has temporarily been made illegal to drive except in an emergency or to seek shelter, in order to keep the roads free for emergency vehicles.
Cold temperatures reached deep into the US south-east.
The weather has been blamed for at least 16 deaths in recent days, including:
The state of Minnesota and the city of Chicago, Illinois, have ordered all schools closed.
It was so cold that even the polar bear at Chicago's Lincoln Park Zoo was kept indoors, CNN reports.
In Kentucky, an inmate who escaped a minimum security prison turned himself in to get out of the cold, the Associated Press reported.
Some relief was in sight in the Midwest, as the cold air pattern moved eastward, the National Weather Service said.