LOS ANGELES (Reuters) - The authorities in southern California ordered the evacuation of 82,000 people on Tuesday (Aug 16), after a wildfire broke out in a mountain pass and rapidly engulfed 3,642ha, an official said.

Officials said 700 firefighters were battling the blaze in an area called the Cajon Pass, the latest in a series of wildfires that have blackened nearly 121,400ha of the drought-parched US West. "It is a very fast-moving fire, it has wind behind it," said US Forest Service spokesman Lyn Sieliet.

The so-called Bluecut Fire erupted in heavy brush just west of Interstate 15, the main freeway between Las Vegas and the Los Angeles area, forcing the closure of one stretch of the highway.

The blaze prompted the orders for residents of the community of Wrightwood, about 120km east of Los Angeles, to leave their homes, said Ms Lynne Tolmachoff, of the California Department of Forestry and Fire Protection (Cal Fire).

In all, about 82,000 people were ordered to flee, as flames destroyed an unknown number of houses, the Cal Fire spokesman said by telephone.

The Bluecut Fire, whose cause officials said they were still investigating, came as crews more than 970km to the north-west began to make headway against a Northern California wildfire that has destroyed more than 175 homes and businesses.

The so-called Clayton Fire was 35 per cent contained, according to Cal Fire. It has charred 1,620ha in and around the community of Lower Lake, forcing hundreds of people to flee.

Damin Pashilk, a 40-year-old arrested on suspicion of setting that blaze, and several others in the area over the past year, is set to appear in court on Wednesday.

Fierce winds fanned the fire, which threatened about 1,500 structures at its peak, after it sparked on Saturday evening. As of Tuesday evening, only 380 buildings were in danger, according to Cal Fire. There were no reports of casualties.

California Governor Jerry Brown declared a state of emergency in San Bernardino County for the Bluecut Fire, which allows state agencies to come to the assistance of local officials. On Monday, Brown issued emergency declarations for the Clayton fire and another in Central California, the so-called Chimney fire.

The Chimney Fire was 20 percent contained by Tuesday evening, after scorching 2,792ha since Saturday. It has destroyed about 40 structures.