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

This NASA Earth Observatory satellite image obtained July 18, 2021 shows smoke soaring hundreds of miles from wildfires in the US and Canadian Northwest
This NASA Earth Observatory satellite image obtained July 18, 2021 shows smoke soaring hundreds of miles from wildfires in the US and Canadian Northwest NASA Earth Observatory / Lauren DAUPIN

Bootleg, the largest of 80 major fires now active in the US, spread overnight from 274,000 acres to 290,000 acres -- three times the size of the metropolis of Detroit, officials said.

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

Smoldering trees in the Bootleg Fire on July 17, 2021 near Klamath Falls, Oregon
Smoldering trees in the Bootleg Fire on July 17, 2021 near Klamath Falls, Oregon US Forest Service / Handout

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 miles to the northeast.

A firefighter and rig during night operations on the night of July 17 at the Bootleg Fire, near Klamath Falls, Oregon
Wildfires across the U.S. continue to threaten homes and have affected commercial and cargo flights due to jet fuel shortages. US Forest Service / Handout

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

Heavy winds and widespread lightning storms remained a serious threat.

More than 2,100 US firefighters in southern Oregon continue to fight the massive Bootleg Fire
More than 2,100 US firefighters in southern Oregon continue to fight the massive Bootleg Fire AUDIO NETWORK

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 20,000 acres, 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 Center 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 2.5 million acres already having burned this year.