The entire population of the Canadian city of Fort McMurray was ordered to leave their homes late on Tuesday as a massive wildfire swept through Alberta province's oil sands region.

More than 80,000 residents were ordered to flee after an earlier evacuation order was extended to tens of thousands more people as flames continued to make their way into the city.

No casualties have been reported but damage has been extensive, with petrol stations exploding and a hotel and one of the town's many motor home parks going up in flames, local media said.

The air over the city was thick with black smoke.

"All of Fort McMurray is under a mandatory evacuation order," Alberta emergency services said, after previously indicating that the northern edge of the fire was "growing rapidly”.

Scott Long, of Alberta Emergency Management, said the flames had burned a number of structures, but couldn't say how many.

The airport was still open but the hospital had to close.

Alberta Premier, Rachel Notley, said officials were doing all they could to ensure people's safety and said they were looking into the possibility of an airlift for residents with medical issues.

"I know that it's a very scary time," Notley told a press conference.

“Our focus is completely and entirely right now on ensuring the safety of people, of getting them out of the city and ensuring that they are safe and secure."

Authorities urged residents to head towards evacuation centres as the city reeled from what Notley called the province's largest ever evacuation.

Prime Minister Justin Trudeau said that he had called Notley to offer federal aid to the province.

"My thoughts are with people affected by the fire in Fort McMurray tonight. Stay safe and remember to follow evacuation orders," he tweeted.

Helicopters and firefighters

Long lines of cars travelled north via the city's main highway, while flames ravaged the embankment on the side of the road. Police closed the southbound lanes.

"Be patient, drive safely and please give way to emergency vehicles," an evacuation notice read.

The fire, which was contained south of Fort McMurray until Monday, was pushed towards the city by 50km/hr winds and quickly reached homes, helped by a drought in Alberta.

The province saw record temperatures of nearly 30C.

The fire quickly expanded, with blazes forming in several places, forcing the city's evacuation.

Bruce Mayer, assistant deputy minister of agriculture and forestry, said nine air tankers, a dozen helicopters and about a hundred firefighters were battling the flames, with reinforcements on the way.

Some 160 police officers were mobilised to implement the evacuation, according to Notley.

Oil companies, crucial to the region's economy, set up emergency shelters in their huge bungalow communities for Canadian and foreign workers.

Source: Agencies