* Fort McMurray residents will be unable to return for a while
* Ground evacuation of those to the north expected early Friday
* Flames spread south, threaten two oil sands sites - officials (Recasts with warnings of no quick return to city, details on oil facilities, update from emergency officials in Fort McMurray)
By Rod Nickel and Liz Hampton
CONKLIN/LAC LA BICHE, Alberta, May 5 (Reuters) - The 88,000 residents who fled a wildfire that has ravaged the Canadian oil town of Fort McMurray in Alberta will not be able to return home anytime soon, officials warned on Thursday, even as the inferno edged slowly south.
The out-of-control blaze has consumed entire neighborhoods of Fort McMurray in Canada's energy heartland and officials warn its spread now threatens two oil sands sites south of the city.
The wildfire has already forced precautionary production cuts or shutdowns at about a dozen major facilities, eating into a global crude surplus and supporting oil prices this week.
"The damage to the community of Fort McMurray is extensive and the city is not safe for residents," said Alberta Premier Rachel Notley in a press briefing late Thursday, as those stranded in camps and on the roadside to the north of the city clamored for answers.
"It is simply not possible, nor is it responsible to speculate on a time when citizens will be able to return. We do know that it will not be a matter of days," she said.
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, had been destroyed by Wednesday morning. Officials declined on Thursday to estimate how many more had been lost.
The communities of Anzac and Gregoire Lake Estates about 50 kilometers (31 miles) south of Fort McMurray were "under extreme threat," late Thursday, as the flames spread to the southeast.
CNOOC Nexen's Long Lake oil sands facility and Athabasca Oil's Hangingstone project are also in danger as winds blow southward, according to emergency officials.
There have been no known casualties from the blaze itself, but fatalities were reported in a car crash along the evacuation route.
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 massive conflagration.
The blaze, which erupted on Sunday, grew more than tenfold 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.
The dry weather conditions prompted the province to issue a fire ban for parks and protected areas on Thursday.
For those stranded north of Fort McMurray, there was a hint of good news. With the fire moving to the southeast, officials are hoping to begin a ground evacuation from the north on Friday morning and briefly re-open the main highway through the city to let people drive south.
On Thursday, frustration for thousands stranded to the north was growing, with some venting online and demanding answers.
One twitter user posted a message saying, "NO ONE IS TELLING US ANYTHING!! We're just sitting in a camp praying to get out!! Give us answers!!! Please."
The premier said that a government airlift of those cut off to the north was going smoothly and that about 4,000 people had already been evacuated to the cities of Edmonton and Calgary as of late Thursday.
Closer to the scene, hundreds filled a community center on Thursday in Lac La Biche, a community 290 km (180 miles) south of Fort McMurray. Many were second-round evacuees ordered to relocate from temporary refuges closer to Fort McMurray on Wednesday night as the flames spread.
Kirby Abo, who came from Fort McMurray with his wife and three children, said he worried that his job in a recycling depot may no longer exist when he returns home.
"I think it's going to be a ghost town for quite a while," he said.
Fort McMurray's mayor in a television interview acknowledged the city faces a long road to recovery, saying that "what comes next is absolutely daunting, but not insurmountable."
The winds gave the city a reprieve on Thursday by driving the fire to the southeast, away from areas with the most dwellings. But officials warned the unpredictable weather could quickly shift and that gusting winds have been very challenging for firefighters. Properties near green areas in Fort McMurray remain at risk, they said.
With additional reporting by Ethan Lou, Andrea Hopkins, Allison Martell, Amran Abocar, Jeffrey Hodgson and Euan Rocha in Toronto, Nia Williams in Calgary and Julie Gordon in Vancouver; Writing by Andrea Hopkins, Dan Whitcomb and Euan Rocha; Editing by Cynthia Osterman, Andrew Hay and Tom Hogue