Residents of Yellowknife, one of the largest cities in Canada's far north, were ordered Wednesday to flee by road or air amid warnings that wildfires could reach it by the weekend.

"Unfortunately, our wildfire situation has taken another turn for the worst with a fire burning west of Yellowknife now representing a real threat to the city," Shane Thompson, the Northwest Territories' environment minister, told a news conference.

He ordered the city's nearly 20,000 residents to leave by Friday noon by vehicle or air.