The wildfire, which has forced the evacuation of the city of Fort McMurray, covered more than 200,000 hectares (494,000 acres) by midnight on Saturday, thus doubling in size in one day, according to the Alberta Emergency Management Agency.

High temperatures, dry conditions and strong winds are providing ideal conditions for the fire in the Alberta oil sands region. The inferno - now roughly the size of Greater London - is one of several currently burning in the province.

"This remains a big, out of control, dangerous fire," said Public Safety Minister Ralph Goodale. His comment was echoed by Alberta Premier Rachel Notley.

"In no way is this fire under control," Notley said, adding that the evacuation of northern work camps, where many Fort McMurray residents have fled, was planned to be completed by Sunday. She said some 12,000 people had been airlifted from the region over the past two days, and about 7,000 had managed to leave the region safely in highway convoys escorted by police.

Mass evacuation

Police in Fort McMurray have been going door to door to find any residents who have not yet left the city of 100,000. More than 80,000 have already headed for safety. Officials say it is not possible to predict when they can return, with the city's power grid damaged and the water currently undrinkable.

No deaths directly linked to the blaze have been recorded since the fires in Alberta broke out a week ago. However, there has been serious material damage, with at least 1,600 homes and other buildings burnt out.

Chad Morrison of Alberta Wildfire said a fire of these dimensions in forested areas could continue burning for months. He said that the fires in the province could be slowed by cooler conditions forecast in the coming days, but added that major rainfall would be needed to have any impact on the severity of the blazes.

Although the fire is expected to reach the edges of the Suncor oil sands facility, about 25 kilometers (15 miles) north of Fort McMurray, Morrison said it wasn't likely that it would affect the oil sands mines north of Suncor.

Efforts are being made to protect the Suncor site, and nonessential staff have been leaving the area. Another oil company operating in the region, Syncrude, said it had also been forced by smoke to shut down its facility 50 kilometers (31 miles) north of Fort McMurray.

The Alberta oil sands contain the third-largest reserves of oil in the world after Saudi Arabia and Venezuela. The fire has resulted in a cut of at least a quarter in Canada's oil output, compounding the economic damage from the recent fall in oil prices.

The loss in income amounts to tens of millions of dollars a day.

Altogether 43 separate fires are burning across the province, seven of them completely out of control. More than 1,400 firefighters, some 133 helicopters, 200 pieces of heavy equipment and more than 27 air tankers are battling the blazes.

tj/rc (AFP, AP)