Five people are reported to have died of carbon monoxide poisoning in Canada, as thousands of homes are still without power following last weekend's ice storm.
They are among 10 people have died in Canada, while in the United States the death toll has reached at least 17, from traffic accidents and carbon monoxide fatalities.
Quebec police said carbon monoxide poisoning was believed to be the cause of three deaths in a chalet on the province's North Shore.
Earlier, five people were killed in eastern Canada in highway crashes blamed on severe weather conditions.
The ice storm was one of the worst to hit during a Christmas week, and repair crews were working around the clock to restore service.
As temperatures plunged below minus 7C (19F) in Toronto, the authorities reported a dramatic jump in calls for suspected carbon monoxide poisoning, responding to 110 calls in a 24-hour period.
Officials said they typically see 20 such calls a day.
"I understand they want to keep warm, but you cannot do this. This is deadly," Toronto Mayor Rob Ford said on Tuesday as the city issued an extreme cold weather alert.
Fire officials warned residents not to use any appliance that burns inside a home, and even cautioned against using a lot of candles.
In Toronto, about 72,000 customers remained without power on Christmas morning - down from 300,00. Elsewhere in Ontario, about 30,000 customers were still without power.
In Quebec, some 28,000 customers remained without power. In New Brunswick, just under 30,000 customers were still in the dark.
Tens of thousands of homes were still without power yesterday in Michigan, down from more than 500,000 at the storm's peak. Maine had about 60,000 without power, down from more than 100,000.
Canadian utility officials warned that some customers could be without power until Saturday.