Canadian police have led convoys of cars through the oil city of Fort McMurray after an out-of-control blaze destroyed entire neighbourhoods and forced tens of thousands of people to flee.

The fire burned 85,000 hectares in Alberta province, forcing mass evacuations earlier this week, and threatening two oil sands sites south of the city.

While the main fire turned south-east on Thursday, away from Fort McMurray, parts of the city still burned.

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A Royal Canadian Mounted Police spokesman said the convoy of 1,500 vehicles would not be allowed to stop until they passed the mandatory evacuation zone, south of Fort McMurray.

"Things have calmed down in the city a little bit, but guys are out as we speak, fighting fires, trying to protect your property," local fire chief Darby Allen said in a video message to residents posted late on Thursday night.

"The beast is still up, it's surrounding the city, and we're here doing our very best for you."

Meanwhile, around 8,000 people have been airlifted out of the northern enclave on helicopters and planes.

Some 25,000 people had fled north on Tuesday and Wednesday as the blaze closed off their only route south, according to officials.

Although the cause of the fire was not known, tinder-dry brush, low humidity, and hot, gusting winds made it nearly impossible to control.

The blaze, which erupted last Sunday, grew more than tenfold from 7,500 hectares on Wednesday to some 85,000 hectares on Thursday, an area nearly 10 times the size of Manhattan.

The Government has declared a state of emergency in Alberta, home to one of the world's most prodigious oil industries.

Blaze sparks mass evacuation

The wildfire forced all 88,000 people to flee the western Canadian oil city of Fort McMurray and burned down at least 1,600 structures, including homes and motels.

One particularly hard hit area was the Beacon Hill neighbourhood, some five kilometres from downtown Fort McMurray, where 70 per cent of homes were in ruins.

Even harder hit was Waterways, where nine in 10 homes have been reduced to charred remains.

Sorry, this video has expired Panic as Fort McMurray fires force evacuations

Data has emerged that the emergency has knocked out as much as a third of Canada's daily crude capacity as pipelines are closed near the fires.

While oil sands facilities are not in the fire's path, several production companies and two pipeline operators have curbed activities to take precautions to move workers and others to other areas.

At least 680,000 barrels per day of capacity were offline on Thursday, according to calculations by the Reuters news agency.

Search on for accommodating thousands

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Ms Notley warned evacuees may face a long wait before they will be able to return home.

The damage from the blazes is major and there is no way to predict when any evacuees can go home," she said.

"Unfortunately, we do know that it will not be a matter of days," she told a news conference.

"It is apparent that the damage to the community in Fort McMurray is extensive, and the city is not safe for residents at this time."

Ms Notley said authorities would work to find lodging for evacuees and move forward to get children back to school in other cities.

"I understand the Albertans are scared, tired, and worried about their homes and what the future holds for themselves and their families," she said.

"Trust us that we have your back, that we will be there for you and that we will support you along the way."

As flames fanned south, officials issued mandatory evacuation orders for the Anzac, Gregoire Lake Estates and Fort McMurray First Nation communities located about 50 kilometres south of Fort McMurray.

A Canadian Joint Operations Command aerial photo shows wildfires in Fort McMurray which have burnt through 85,000 hectares. ( Reuters: CF Operations handout )

Officials at the scene were forced to evacuate their makeshift emergency operations centre for the second time in less than a day as the flames spread south.

Officials at the centre said in a tweet that they were relocating to the town of Lac La Biche, about 250 kilometres south of Anzac.

Sorry, this video has expired Briar Stewart at the site of the Fort McMurray wildfire evacuation

Authorities said there had been no known casualties from the blaze itself, but fatalities were reported in at least one car crash among evacuees.

Thousands of people bunked down in arenas, hockey rinks and oil work camps, often short of fuel and food.

Stretches of the highway had been converted into make-shift campgrounds by people in cars, trucks and recreation vehicles, who were fleeing the inferno.

Ms Notley told media that in the Alberta area, 49 wildfires were still burning, including seven that are out of control.

NASA shows a photo of the smoke plumes from the Fort McMurray fires, taken with Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite. ( Supplied: NASA/Jeff Schmaltz )

AFP