Local authorities issued a mandatory order for all of the city on Tuesday, describing it as the biggest evacuation in the province's history.

But Alberta Premier Rachel Notley called for other provinces and the Ottowa government to send assistance.

"We need to find more camps, we have secured spaces for about 6,000 people, we know we need to find more and that work is underway," Notley said.

The 2,650-hectare (6,540-acre) fire, which was initially reported on May 1, has closed off the main southern exit from the city, prompting residents to head north towards the oil sands camps.

Crews had seemed to be making progress controlling the blaze, burning since the weekend, but the situation worsened quickly on Tuesday. By mid-afternoon people from three neighborhoods were told to leave immediately.

A radio reporter on the scene described how the flames were advancing towards local businesses.

"It's chaos on the roads. People are panicking. It's gridlock on the roads. Flames are right next to a gas station," said Carina Van Heerde with radio station KAOS.

Local resident Nick Sanders told Reuters: "There's lots of smoke, its quite bad and hanging over the city. Where there are trees in the distance you can see the fire."

Pictures posted on Twitter showed long lines of traffic and skies darkened by thick smoke, as flames licked the edges of roads.

Officials said no one had been injured in the fire and open fires had been banned, due to the threat.

The fire has been blamed on unseasonably hot temperatures and dry conditions in much of Alberta.

This is the second major fire around the city in less than a year. Last May, wildfires in the area led to the evacuation of hundreds of workers from Canada's energy heartland.

mm/rc (AP, Reuters)