Canadian fire crews on Thursday battled to prevent wildfires from reaching the northern city of Yellowknife, where all 20,000 residents are leaving by car and plane 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.

"Very tough days ahead — with two days of northwest to west-northwest winds on Friday and Saturday, which would push fire towards Yellowknife," the territorial fire service said in a statement on Facebook.