FORT MCMURRAY, Alberta (AP) -- Alberta has declared a state of emergency as crews frantically held back wildfires that have torched 1,600 homes in Canada's main oil sands city of Fort McMurray, forcing more than 80,000 residents to flee.

Alberta Premier Rachel Notley said fire had destroyed or damaged an estimated 1,600 structures. Flames are being kept from the downtown area thanks to the "herculean'" efforts of firefighters, said Scott Long of the Alberta Emergency Management Agency. No injuries or fire related fatalities have been reported.

The fire appeared near the airport late Wednesday where crews were onsite. All commercial flights in and out of Fort McMurray have been suspended.

Unseasonably hot temperatures combined with dry conditions have transformed the boreal forest in much of Alberta into a tinder box. Fort McMurray is surrounded by wilderness in the heart of Canada's oil sands - the third largest reserves of oil in the world behind Saudi Arabia and Venezuela.

Danielle Larivee, Alberta's minister of municipal affairs, said the fire is actively burning in residential areas. More than 250 firefighters are battling the blaze. An update from the Municipality of Wood Buffalo later in the evening indicated the fire was continuing to claim homes and had destroyed a new school.

Fatalities have been reported from a collision on a nearby highway but she was unaware if it was related to the evacuation or fire.

There were haunting images of scorched trucks, charred homes and telephone poles, burned out from the bottom up, hanging in the wires like little wooden crosses.

Some residents were evacuated for a second time late Wednesday when they were told to leave their emergency accommodations in the nearby hamlet of Anzac.

Officials said changing weather patterns forced the move. There had been 2,500 evacuees registered at the local recreation center, although it was not known how many were still there when they were told to get on buses for Edmonton further to the south.

Alberta Premier Rachel Notley flew up to survey the situation, and tweeted pictures of the fire from above. "The view from the air is heartbreaking," she wrote

The blaze effectively cut Fort McMurray in two late Tuesday, forcing about 10,000 north to the safety of oil sands work camps.

The other 70,000 or so were sent streaming south in a bumper-to-bumper snake line of cars and trucks that stretched beyond the horizon down Highway 63. Some vehicles sat in ditches, the victims of engine trouble or a lack of gas.

Firefighters were working to protect critical infrastructure, including the only bridge across the Athabasca River and Highway 63, the only major route to the city in or out.

Notley called it the biggest evacuation in the history of the province. Federal Public Safety Minister Ralph Goodale called it one of the largest fire evacuations in Canadian history, if not the largest. "It's a community of 88,000 people that's been totally evacuated," Goodale said. "This is going to take a while to recover."

Canadian Prime Minister Justin Trudeau said while the full extent of the damage isn't yet known he called it "absolutely devastating" and said there's a loss on a scale that's hard to imagine. Trudeau said he's offered the province his government's full support. He encouraged Canadians to support friends and donate to the Red Cross.