With oppressively hot, dry weather looming over much of the Western US and Canada on July 18, the enormous “Bootleg Fire” in the US state of Oregon grew again and authorities ordered new evacuations.

Bootleg, the largest of 80 major fires now active in the US, spread overnight from 111,000ha to 117,000ha – three times the size of the metropolis of Detroit, officials said.

Some 2,000 people have had to evacuate, with more following on July 18.

Satellite imagery from the National Weather service showed a huge plume of smoke soaring from Bootleg, in southern Oregon, to the Canadian border, hundreds of kilometres to the northeast.

But, with firefighters making progress on Bootleg’s western flank, overall containment of the blaze more than tripled, to 22 per cent.

Heavy winds and widespread lightning storms remained a serious threat.

Firefighters blamed lightning strikes for a fast-growing blaze in California’s Lake Tahoe tourist area. The so-called “Tamarack Fire”, fanned by fierce winds, has grown explosively to more than 8,000ha, with zero containment so far.

The small nearby community of Markleeville, on the Nevada border, has been evacuated.

Scientists say climate change amplifies droughts which create ideal conditions for wildfires to spread.

The National Interagency Fire Centre said the outlook was for “very hot, dry and unstable conditions across the inland Pacific Northwest, Northern Rockies and Plains into northern Minnesota”.

It said nearly 20,000 firefighters and support personnel are struggling to contain fires raging across the Western states, with more than one million hectares already having burned this year.

Firefighters in Canada, meanwhile, continued to battle dozens of blazes, including some 20 new ones in British Columbia province and about 15 new ones in northwest Ontario province.

Authorities in that province said a firefighter had died in hospital of an unspecified “medical emergency”.