A "heat dome" over western Canada and the US Pacific northwest sent temperatures soaring to new highs, triggering heat warnings from Oregon to Canada's Arctic territories on Sunday.

Hotspot Lytton in British Columbia -- about 250 kilometres (155 miles) northeast of Vancouver -- broke the record "for Canada's all time maximum high" with a temperature of 46.6 degrees Celsius (116 Fahrenheit), said Environment Canada.

More than 40 new temperature highs were recorded throughout the province over the weekend, including in the ski resort town of Whistler. And the high-pressure ridge trapping warm air in the region is expected to continue breaking more records throughout the week.

Environment Canada issued alerts for British Columbia, Alberta, and parts of Saskatchewan, Yukon and the Northwest Territories.

"A prolonged, dangerous, and historic heatwave will persist through this week," it said, forecasting temperatures near 40 degrees Celsius (104 Fahrenheit) in several regions, or 10-15 degrees Celsius hotter than normal.

The US National Weather Service issued a similar warning about a "dangerous heat wave" that could see record temperatures rise to more than 30 degrees Fahrenheit above normal in parts of Washington and Oregon states.

"The historic Northwest heatwave will continue through much of the upcoming week, with numerous daily, monthly and even all time records likely to be set," it said in a statement.

Monday is expected to be the hottest day in big cities such as Seattle and Portland, with all-time record highs likely in both cities.

The highest temperature previously recorded in Canada was 45 degrees Celsius in two towns in southeastern Saskatchewan in July 1937.

"I like to break a record, but this is like shattering and pulverising them," Environment Canada senior climatologist David Phillips told broadcaster CTV. "It's warmer in parts of western Canada than in Dubai."

Wildfire risks are elevated, and water levels in lakes and rivers are lower.

Stores reportedly sold out of portable air conditioners and fans, while cities opened emergency cooling centers and outreach workers took to the streets to hand out bottles of water and hats.

Several Covid-19 vaccination clinics were cancelled and schools announced they would close on Monday.

The British Columbia power utility, meanwhile, said electricity demand has soared to record levels as residents sought to keep cool.