82,000 evacuated in US fires

Dozens of homes are destroyed and 82,000 people have been evacuated as a wildfire burns out of control in a rural mountain area in southern California.

More than 82,000 people in southern California have been ordered to flee a raging wildfire burning out of control in a rural mountain area.

The Blue Cut fire in Cajon Pass, about 100km east of Los Angeles in San Bernardino County, mushroomed into an inferno covering more than 121sq/km, the National Wildfire Co-ordinating Group said.

More than 82,000 people were given a mandatory evacuation order on Wednesday in the face of what authorities called an "imminent threat to public safety, rail traffic and structures".

News videos showed houses on fire and at least one local business, a well-known roadside diner, has been destroyed in the blaze, according to the Los Angeles Times.

Amid desperate efforts to ensure evacuations and control the fire there was no official tally of property damage, but authorities spoke of dozens of homes destroyed.

"There will be a lot of families that come home to nothing," San Bernardino County Fire Chief Mark Hartwig told media.

The fire closed multiple roads, including a major interstate highway linking Los Angeles and Las Vegas.

Firefighter veterans said hot weather, drought-dry brush, and rugged terrain which has funnelled winds and thwarted firefighting efforts, have combined to create ideal conditions for a firestorm.

"In my 40 years of fighting fires, I have never seen such extreme fire behaviour," fire incident commander Mike Wakoski told Southern California Public Radio.

More than 1300 firefighters were battling the fire but had yet to gain control, authorities said.