By Rod Nickel and Liz Hampton
LAC LA BICHE, Alberta (Reuters) - A raging Canadian wildfire grew explosively on Saturday as hot, dry winds pushed the blaze across the energy heartland of Alberta and smoke forced the shutdown of a major oil sands project.
The fire that has already prompted the evacuation of 88,000 people from the city of Fort McMurray was on its way to doubling in size on Saturday, the seventh day of what is expected to be the costliest natural disaster in Canada's history.
Police escorted another convoy of evacuees out of the oil sands region north of Fort McMurray, taking them on a harrowing journey through burned out parts of the city and billowing smoke. Some 1,600 structures are believed to have been lost.
With temperatures on Saturday expected to rise as high as 28 Celsius (82 Fahrenheit), officials said the weather was hindering efforts to fight the wildfire.
"It is a dangerous, unpredictable fire, an absolutely vicious fire that is feeding off of an extremely dry boreal forest," Canadian Public Safety Minister Ralph Goodale told a media briefing.
The fire had scorched at least 156,000 hectares (385,000 acres) by Saturday morning, the Alberta government said. Officials warned late on Friday that the area affected by the fire, which they then said was 101,000 hectares, could double in size by the end of Saturday.
More than 500 firefighters are battling the blaze in and around Fort McMurray, along with 15 helicopters and 14 air tankers, the Alberta government said.
Within Fort McMurray, visibility is often less than 30 feet (9 meters) due to the smoke, making it still very dangerous to circulate in the city, Royal Canadian Mounted Police Inspector Kevin Kunetzki told reporters at a highway checkpoint.
Despite the fire's rapid spread, Goodale said there was no indication that oil infrastructure was at risk.
But the Syncrude oil sands project said Saturday it will shut down its northern Alberta operation and remove all personnel from the site due to smoke. There was no imminent threat from the fire.
At least 10 oil sand operators have cut production due to evacuations and other emergency measures that complicated delivery of petroleum by rail, pipeline and highway.
About half of Canada's oil sands production capacity has been taken offline by the conflagration, according to a Reuters estimate.
Earlier in the week most evacuees headed south by car on Alberta Highway 63, the only land route out of the area, in a slow-moving exodus that left many temporarily stranded on the roadside as they ran out of gasoline.
But other residents who initially sought shelter in oil camps and settlements north of the city found themselves cut off in overcrowded conditions. They were forced on Friday and Saturday to retrace their route back through Fort McMurray on Highway 63 as flames continued to spread.
Goodale said it was important to move those people south, given the risk that winds could shift and push the fire to the northwest of its current location.
The full extent of property losses in Fort McMurray has yet to be determined, but one analyst estimated insurance losses could exceed C$9 billion ($7 billion).
Entire neighborhoods were reduced to ruins, but most evacuees fled without knowing the fate of their own homes. The majority got away with few possessions, some forced to leave pets behind.
Stephane Dumais, thumbing through his insurance documents at an evacuation center at Lac La Biche, said he has thought about moving away. But the idea doesn't sit well with the heavy equipment operator for a logging company.
"To me that's like giving up on my city," he said. "As long as it takes to rebuild it, let's work together. It's not going to be the same as it used to be."
(Additional reporting by Ethan Lou in Toronto,; Writing by Jeffrey Hodgson; Editing by Digby Lidstone and Mary Milliken)