Canadian wildfire explodes in size, forces more evacuations

* Fire conditions extreme, with low humidity, gusting winds

* Emergency tankers helping refuel stranded evacuees on highway (Adds fire has grown 10 times in size, government airlifting evacuees)

By Rod Nickel

LAC LA BICHE, Alberta, May 5 (Reuters) - A catastrophic wildfire that has forced all 88,000 residents to flee Fort McMurray in Alberta, Canada exploded tenfold in size on Thursday, cutting off evacuees in camps and shelters north of the city.

The out-of-control blaze has burned down entire neighborhoods of Fort McMurray in Canada's energy heartland and forced a precautionary shutdown of some oil production, driving up global oil prices.

Three days after the residents were ordered to leave Fort McMurray, firefighters were still battling to protect homes, businesses and other structures from the flames. More than 1,600 structures, including hundreds of homes, have been destroyed.

Although the cause of the fire was unknown, officials said tinder-dry brush, low humidity and hot, gusting winds left crews unable to stop the flames.

The blaze, which erupted on Sunday, grew from 18,500 acres (7,500 hectares) on Wednesday to some 210,000 acres (85,000 hectares) on Thursday, an area roughly 10 times the size of Manhattan (Hamburg: 32U.HM - news) .

"What people in that region have gone through in the last couple of days is literally hell on earth," Rona Ambrose, leader of the opposition Conservative Party and an Albertan, fighting back tears as she addressed the Canadian Parliament in Ottawa.

Fire has intermittently blocked the only route south toward major cities, so thousands of evacuees fled north toward oil camps and a few small settlements but found themselves with no road route out.

Some 20,000 people were stranded in oil camps, makeshift shelters and on roadsides north of the city where the flames cut them off from Fort McMurray. Most of Alberta's oil sands facilities are north of the city and not in the path of the flames.

Evacuee Jason Blair said he only had enough time to grab a few belongings before driving north to a Canadian Natural Resources Ltd facility.

"For some reason I really wanted my son's first pair of shoes," he told CBC television.

An airlift of evacuees began from oil facility airstrips on Thursday.

Canadian Natural Resources said it airlifted about 2,600 people over the last 24 hours to Edmonton and Calgary, including its own workers, to make room for more evacuees.

Frightened evacuees north of the city took to Twitter (Xetra: A1W6XZ - news) , asking when they would be able to drive south and whether areas to the north were safe.

"We're just sitting in a camp praying to get out!! Give us answers!!! Please," Twitter user @jennimac780 told the regional government.

"We haven't forgotten about you and you're safe," the government said on Twitter.

The winds gave the city a brief reprieve on Thursday by driving the fire to the southeast, away from populated areas. But officials warned that the unpredictable weather could shift again.

The winds pushed flames toward the local airport, which suffered minor damage and was open for limited non-commercial operations, officials said.

A makeshift emergency operations center at the airport was evacuated for the second time in less than a day.

At least 640,000 barrels per day of crude output is offline, according to Reuters calculations, roughly 16 percent of Canada's crude production. The outage is expected to climb as major players in the region cut production.

The forecast has called for cooler temperatures and a possibility of rain, offering hope that controlling the blaze could become easier. Meteorologists put the chance of rain at 30 percent on Thursday.

Authorities said there had been no known casualties from the blaze itself, but fatalities were reported in at least one vehicle crash along the evacuation route.

(Reporting by Ethan Lou, Andrea Hopkins, Allison Martell and Amran Abocar in Toronto, Nia Williams in Calgary and Liz Hampton in Edmonton; Writing by Andrea Hopkins and Dan Whitcomb; Editing by Jeffrey Benkoe and Cynthia Osterman)