Whipped up by wind and fuelled by tinder dry conditions, the wildfire in Fort McMurray, Alta., grew to about 1,000 square kilometres on Friday.
An expert said it's a dangerous fire because of its location, not necessarily because of its size.
"Let's put this into perspective. That is a high-priority area," said Marc Mousseau of the Canadian Interagency Forest Fire Centre in Winnipeg.
"If you get a fire on the Saskatchewan-Manitoba-Nunavut border, that thing could be 300,000 hectares (3,000 square kilometres) and nobody would even know because there's nobody up there and it's zero priority."
Mousseau said that's why the size of a fire isn't always the most important factor in setting firefighting priorities.
"Is it a large fire that caused a lot of concern or is it a large fire in the middle of nowhere that's roaming around for three months and they're tracking it with satellites? In other words, they're not even looking at it."
Mousseau uses the so-called Great Miramichi Fire of 1825 as an example. It's estimated that the fire destroyed about 12,000 square kilometres in northern New Brunswick. At least 160 people were killed.
In 2011, a fire destroyed about 7,000 square kilometres in northern Alberta. The Richardson backcountry fire was about 60 kilometres north of Fort McMurray and has been described as the largest fire in Alberta's modern history.
But Mousseau suggests it may have slipped under the radar for the public because it happened at the same time as a devastating fire in Slave Lake, Alta.
The Slave Lake fire only covered about 47 square kilometres, but forced more than 10,000 to flee the community. One-third of Slave Lake, more than 500 homes and buildings, including the town hall, were damaged or destroyed.
A report prepared by consulting firm KPMG on the Slave Lake fire said: "Everyone was caught off guard by how fast the fires advanced with this wind behind them."
On its website, the B.C. Wildfire Service lists large wildfires, including the fire in the Kelowna area in 2003.
The Okanagan Mountain Park fire was more than 250 square kilometres. It forced 33,050 people out of their homes, mostly in Kelowna, and nearly 240 homes were lost or damaged. Three firefighters were killed.
The service describes it as "the most significant interface wildfire event in B.C. history," interface being the area where people and the forest meet.
