Canadian fire crews on Thursday battled to prevent wildfires from reaching the northern city of Yellowknife, where all 20,000 residents are leaving by cars and flights after an evacuation order was declared.

Water bombers flew low over Yellowknife as thick smoke blanketed the capital of the vast and sparsely populated Northwest Territories. Officials say the fire, which is moving slowly, is now 15 kilometers northwest of the city and could reach the outskirts by Saturday if there is no rain.

In the Pacific province of British Columbia, which has suffered unusually intense blazes this year, officials warned residents to prepare for extreme fire conditions.

"This weather event has the potential to be the most challenging 24 to 48 hours of the summer from a fire perspective," wildfire service director Cliff Chapman told reporters. "We are expecting significant growth, and we are expecting our resources to be challenged from north to south."

In Yellowknife, hundreds of people lined up outside a local high school waiting to be taken to the airport for one of the five evacuation flights planned on Thursday to the neighboring province of Alberta.

The Northwest Territories have limited infrastructure, and there is only one two-lane road out of Yellowknife to the province of Alberta to the south.

Canadian Prime Minister Justin Trudeau convened an emergency meeting on Thursday to discuss the wildfire crisis in the Northwest Territories.

Defence Minister Bill Blair, speaking to the Canadian Broadcasting Corp (CBC) after the meeting, said the federal government was closely monitoring the evacuations and was prepared to quickly airlift residents if land routes get cut off.

According to the Canadian Interagency Forest Fire Centre, there were around 1,000 active forest fires in Canada, 265 of which were burning in the Northwest Territories.

Shane Thompson, the territorial environment minister, said the evacuation order had been issued late Wednesday to give people time to get out before the weather turned bad.

"The urgency is, fire changes drastically ... the conditions are in our favor right now, but that will change on Saturday," he told the CBC.

In total, about 65 percent of the Territories population of 46,000 people would be evacuated, he said. The deadline for residents to leave Yellowknife is noon on Friday (1800 GMT).

(With input from Reuters)

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