Officials in western Canada's British Columbia implored tens of thousands of residents to heed warnings and evacuate Saturday as "severe and fast changing" wildfires threatened large parts of the scenic Okanagan Valley, including the city of Kelowna.

The situation in the popular boating and hiking destination was "highly dynamic," said Bowinn Ma, the province's minister of emergency management.

Around 30,000 people were under evacuation orders while another 36,000 were under alert to be ready to flee, she said.

"We cannot stress strongly enough how critical it is to follow evacuation orders when they are issued," Ma said at an afternoon news conference.

"They are a matter of life and death not only for the people in those properties, but also for the first responders who will often go back to try to implore people to leave."

Kelowna, a city of 150,000, was choked with thick smoke as it became the latest population center hit in a summer of dramatic wildfires across Canada that has left millions of acres scorched.

Prime Minister Justin Trudeau said he had spoken with British Columbia Premier David Eby about the "rapidly evolving and incredibly devastating wildfire situation" and pledged federal resources in responding to the disaster.

Blazes far away in the neighboring Northwest Territories have meanwhile prompted the evacuation of regional capital Yellowknife, leaving the remote city of some 20,000 largely a ghost town.

Winds have been fanning the wildfires towards Yellowknife, but Saturday saw some relief after overnight rain brought a sharp dip in temperatures.

Since the evacuation was ordered Wednesday, most people have fled by road with several thousand taking emergency flights, Northwest Territories environment minister Shane Thompson said Saturday on X, the platform formerly known as Twitter.

"Approximately 1,000 essential staff remaining in the city and surrounding area," he added.

Those crews were remaining to erect defenses from the flames, while water bombers have been seen flying low over the city, with the Canadian military also helping out.

- 'Incredible' exodus -

Tony Whitford, a former commissioner for the Northwest Territories and a longtime resident of Yellowknife, arrived in the city of Calgary on one of the first flights out and gave the evacuation high marks.

"My compliments to them all," Whitford, who is 82 and wheelchair-bound, said of the organizers. "It's so complex -- 20,000 people -- it's incredible. It went smoothly."

Several towns and Indigenous communities were evacuated earlier. The exodus from Yellowknife means half the population of the near-Arctic territory has been displaced.

The ongoing fires have caused "terrible loss," Trudeau told reporters after meeting Yellowknife evacuees Friday as they arrived in Edmonton, Alberta, with no idea when they may return home.

Martha Kanatsiak, who has lived in Yellowknife for 28 years, arrived late Friday in Calgary.

"I'm okay, but I feel sad and depressed and worried. I never saw something like this," the 59-year-old Inuit retiree told AFP.

Some 40 flights carrying around 3,500 passengers from Yellowknife have arrived in Calgary, said officials in the city, which has made nearly 500 hotel rooms available.

- Northwest US threat -

In British Columbia, blazes have already destroyed several properties in West Kelowna, separated by Okanagan Lake from its larger, eponymous neighbor.

Among them is the Lake Okanagan Resort, according to local media, which is known for having hosted high-profile politicians such as British prime minister Margaret Thatcher.

Eby on Saturday announced an emergency order halting non-essential visits to the area.

The order, which bans visitors from checking in at hotels and other temporary accommodations, covers Kelowna and the nearby towns of Kamloops, Oliver, Penticton and Vernon as well as Osoyoos near the US border.

"If you are currently in accommodations in these areas, we are asking you to voluntarily check out early and free up those spaces for evacuees and responders," Ma added.

Meanwhile, across the border in the United States, several thousand people were forced to flee wildfires in Washington state, with at least one death reported, local media said.

An evacuation was ordered for Medical Lake, a town outside Spokane and next to a US Air Force base, while a section of the vital I-90 highway was closed, authorities said.

Canada is experiencing a record-setting wildfire season, with official estimates of over 14 million hectares (34.6 million acres) already burned -- roughly the size of Greece and almost twice the area of the last record of 7.3 million hectares. Four people have died so far.

Scientists say human-caused global warming is exacerbating natural hazards, making them both more frequent and more deadly.