Growing wildfires threatened Canada's oil sands region on Tuesday, destroying a remote lodge used to house hundreds of industry workers and forcing thousands at other facilities to be evacuated.

Overnight, about 8,000 workers were ordered out of the remote area north of the blaze-hit city of Fort McMurray after fires spread and intensified, Alberta Premier Rachel Notley told a press conference.

The sprawling Blacksand Executive Lodge with 665 rooms was destroyed. Two others on the same road with a total of 4,000 rooms were at risk.

"Yesterday morning we anticipated a very active fire day and," she said, "that's exactly what we got."

"We expect fire growth at many of these camps today," she added.

Some 100,000 residents and oil workers had already been evacuated from Fort McMurray and its surroundings two weeks ago, as the flames advanced.

Eight new fires sprung up over the previous 24 hours, bringing to 19 the total number burning in the province. Five of those were burning out of control.

The largest of these, in and around Fort McMurray, has grown to 355,000 hectares (877,000 acres), which represents "significant growth from yesterday," Notley said.

In the city itself, two explosions damaged 10 homes. Ensuing spot fires were quickly put out and nobody was injured, she said.

- No relief -

Across the rugged province that flanks the eastern slopes of the Rocky Mountains, there are nearly 2,000 firefighters, more than 160 helicopters, and 29 air tankers battling the blazes.

Air quality in the north -- compromised by the thick, black smoke -- remains at more than three times the acceptable levels, posing a risk to firefighters and delaying both repairs to damaged Fort McMurray infrastructure and the eventual return of tens of thousands of residents.

A plan to reopen retail outlets in order to serve residents upon their return has been put on hold, and some 400 people brought in to restore the city's hospital had to be evacuated.

An assessment of the damage in the city is almost complete, Notley said.

She said 89 percent of structures were deemed to be "safe to occupy" while 10 percent had been destroyed in the fires. The remaining structures need further evaluation.

There was no firm word on when residents would be allowed to return.

Overnight westerly winds had pushed the fire, which had been beaten back last week, closer to two major oil facilities operated by Suncor and Syncrude.

Workers had just started trickling back to the area when the latest evacuation was ordered late Monday.

Suncor, Canada's largest petroleum company, was forced to shutter its oil operations almost immediately after getting them back up and running.

It said it was moving its personnel to housing facilities farther north.

And as a precautionary measure, "we have started a staged and orderly shutdown of our base plant operations. There has been no damage to Suncor's assets," the company added in a statement.

Notley said the oil workers' camps were the focus of firefighters' efforts on Tuesday, but that the hot temperatures were a factor.

By midday, winds were starting to blow the fires eastward away from the oil facilities.

And Alberta wildfire manager Chad Morrison said it was expected to reach neighboring Saskatchewan province soon.

He said heavy rains would been needed to slow the spread.

"We don't see any relief at this point," Morrison said.

The fires are expected to have a significant economic impact, with oil production representing about four percent of Canada's gross domestic product.

According to the Conference Board of Canada, oil production was reduced by 1.2 million barrels per day on average, depriving government coffers of an estimated $1 billion in oil royalties.