A wildfire in California has destroyed 15 buildings, injured at least five people and forced the evacuation of 500 homes in several small communities east of Los Angeles.

The fire broke out on Wednesday near a back-country road south of the town of Banning, and by nightfall on Thursday had blackened an estimated 14,000 acres, the Riverside County Fire Department said on its website.

Four fire fighters and one local resident have been hurt in the blaze, which was raging through tinder-dry brush about 136km east of downtown Los Angeles. The extent of their injuries was not immediately known.

As of Thursday evening, a fire fighting force of roughly 1,000 personnel, backed up by more than a dozen water-dropping helicopters and several planes carrying payloads of fire-retardant chemicals, had managed to carve fire breaks enclosing 20% of the blaze. That figure was double the containment estimate issued at the start of the day.

Vista Grande, Mount Edna, Poppet Flats, Twin Pines and Silent Valley were among several communities under mandatory evacuation orders as the fire burned toward Cabazon, a town of 2,500 residents about 32km west of the desert resort of Palm Springs.

Shelters for evacuees had been set up at schools in nearby Hemet and Beaumont.

A number of residents living within the evacuation zone were initially advised to remain inside their homes as approaching flames cut them off from a safe escape route, officials said. Those evacuees have since been moved out of harm's way.

At least 15 structures had been destroyed by the fire, but damage assessment teams were still taking inventory of the property losses. Authorities have not yet determined how the fire started.

The blaze was one of the latest to break out during what experts say could become one of the worst US fire seasons on record.

A Colorado wildfire in June, ranked as that state's most destructive ever, ravaged nearly 500 homes and killed two people. In Arizona, 19 members of an elite fire fighting crew died on 30 June while battling a wildfire.