Oil workers in Canada's western province of Alberta have been ordered to evacuate camps as a resurgent wildfire heads towards them.

The emergency on Monday north of the oil town of Fort McMurray has forced firefighters to shift their focus to protect major oil facilities.

The blaze, which continues to burn uncontrolled, now covers 285,000 hectares (704,000 acres), officials said.

By Monday evening, it was moving at 30 to 40 metres a minute north of Fort McMurray and had jumped a critical firebreak to push into the oil sand camp areas.

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"The urgency we're looking at is with regards to the oil gas infrastructure," Scott Long, executive director of the Alberta Emergency Management Agency, told reporters in Edmonton, adding that Fort McMurray itself appeared to be safe for now.

Hundreds of workers in the camps close to the flames were ordered to move out while thousands more were put on standby. There are 12 oil sands camps in the area.

Chad Morrison, Alberta's manager of wildfire prevention, said the blaze was expected to slow into the evening and that it was unclear if it would reach the major oil sand facilities, though responders were preparing for that eventuality.

"When you have this type of extreme fire behaviour, it doesn't matter what tankers you put in front of it, or how many helicopters, Mother Nature is going to continue to move that fire forward," Morrison said.

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Roughly a million barrels a day of oil sands crude production was shut in as a precaution and because of disruptions to regional pipelines, and much of that production remains offline.

Canadian Finance Minister Bill Morneau told CBC News that the Fort McMurray fire would be a challenge to the economy as well as a human challenge, but he had no price tag yet on how much the disaster would cost the federal government.

About 80,000 people fled the area nearly two weeks ago .The fire destroyed more than 2,400 structures in Fort McMurray and the thousands of residents who were moved out continue to live in temporary shelters.

Officials said there was still no timeline on when residents could return.

The wildfire still covers more than 2,000 square kilometres and is expected to burn for months.

An aerial view of the effect of the wildfire that forced the mass evacuation [Jason Franson/Reuters]

Source: Agencies