An uncontrolled wildfire burning near Fort McMurray in northern Alberta, the heart of Canada's oil sands region, has forced the evacuation of nearly all the city's 80,000 residents, local authorities said on Tuesday.

However, the 2,650-hectare (6,540-acre) fire, which was discovered on May 1, is not close to any oil sands facilities, according to Alberta government online maps.

The blaze, which started southwest of Fort McMurray, spread rapidly on Tuesday to the outskirts of the city, forcing the evacuation of the downtown area and almost every community in the lower town on the banks of the Athabasca River.

TV footage and photographs on Twitter showed flames and smoke billowing over the city and traffic heading north on the highway to safety, while CTV News reported a trailer park had been destroyed.

Some residents were evacuated to Noralta Lodge, an oil sands camp 21 km (13 miles) north of Fort McMurray.

Earlier on Tuesday afternoon the wildfire jumped the river to spread to the east bank and breached Highway 63, the main artery south from the isolated city, which is located around 430 km (267 miles) northeast of Alberta's capital, Edmonton.

Chief Darby Allen of the Fort McMurray fire department said temperatures of about 30 Celsius (86 Fahrenheit) and light winds forecast for Wednesday would make the blaze difficult to control.

Most oil sands facilities are to the north and east of the city, with the closest being Suncor Energy's base plant roughly 30 km (17 miles) away. Suncor did not immediately respond to requests for comment.

Will Gibson, a spokesman for the Syncrude project, which has its facility around 40 km (25 miles) north of the city, said operations were unaffected.