The entire population of the Canadian city of Fort McMurray has been forced to evacuate because of a huge wildfire.

Some 80,000 people were told to leave as the blaze swept into the city, which is the gateway to the oil sands region.

Homes, petrol stations and a hotel are among the buildings destroyed in the city, in the province of Alberta.

There was gridlock on roads. Many fled north after flames forced the closure of the main road south. No casualties have been reported so far.

Alberta Premier Rachel Notley called it the "biggest evacuation... in the history of the province".

She said the priority was to get people safely out of the city and find enough spaces in evacuation camps for everybody.

Emergency shelters have been set up in oil sands work camps to the north of Fort McMurray.

One of the town's many motorhome parks has been destroyed.

Brian Jean, the leader of Alberta's opposition party, said: "Our hospital is on fire, where my children were born.

"My home of the last 10 years and the home I had for 15 years before that are both destroyed," he added.

Another resident, Carol Christian, who fled with her son and cat said it was an "overwhelming feeling to think that you'll never see your house again".

She said sitting in traffic was "absolutely horrifying". "You look up and then watch all the trees candle-topping... up the hills where you live, and you're thinking: "Oh my God. We got out just in time."

Canadian Prime Minister Justin Trudeau tweeted his concerns.

Photo: AP

Around 100 firefighters are tackling the blaze, backed up by nine air tankers and more than a dozen helicopters, officials say. Reinforcements are on their way.

The fire started on Sunday south of Fort McMurray, some 380km (235 miles) north of the provincial capital, Edmonton.

Fire officials had the blaze contained until early Tuesday, when high temperatures and strong winds pushed the flames towards the city.