Human-driven climate change made the extreme conditions behind this year's deadly Canadian wildfires twice as likely, according to a new study by the World Weather Attribution (WWA) group.

The analysis found that higher global temperatures caused by burning fossil fuels increased the risk of fire-prone weather in Ontario and the Northwest Territories, where major wildfires have forced evacuations and spread smoke across Canada and parts of the United States.

Researchers said there are currently nearly 700 active wildfires across Canada, with about 3.8 million hectares burned, mainly in boreal forests.

The WWA found that the fire weather seen this year is no longer rare. Without human-caused climate change, similar conditions would have occurred less than once every 40 years.

"The geographic spread of these fires is scary and shows that despite preparedness from wildfire governance, adaptation alone is not enough," Theodore Keeping of Imperial College London said.

"We need to rapidly move away from fossil fuels to avoid events like this becoming even more of a reality."

Co-author Friederike Otto added: "Time and again we see the same results: climate change is a key driver behind uncontrollably large and unprecedented fires."

The study comes as wildfires continue to burn across Canada, including in British Columbia, where thousands of people remain under evacuation orders because of what officials have described as dangerous fire conditions.