Arson blamed for California fire that killed four

A brush fire blamed on arsonists has swept through desert hills in California and killed four firefighters.

Whipped by warm winds after a long, dry summer, the fire roared out of control through about 24,000 acres in less than 24 hours, destroying at least 10 homes and engulfing a firetruck.

By nightfall, the fire line stretched 15 miles along canyons and hills 90 miles east of Los Angeles and 17 miles northwest of Palm Springs.

But Riverside County Fire Department Chief John Hawkins said the more than 1,000 firefighters were finally making progress. He said crews would work through the night despite strong winds and clouds of smoke.

The fire officer said the deaths of the firefighters were being treated as homicide.

"A deliberately set fire that leads to the death of anyone constitutes murder," he said.

A reward of $100,000 was offered to catch the arsonists and Riverside County officials said they had received several tips that were being followed up.

The firefighters who died were caught by erratic winds while trying to save a remote house early in the day. Three died at the scene and a fourth died in the hospital of his injuries. A fifth firefighter was in critical condition, with burns to 95 per cent of his body.

A total of 400 to 1,000 people were trapped in a recreational vehicle park in the hills because firefighters had been unable to get them out.

"They are sheltered in place, which means we could not evacuate them in time. They're going to encounter heat and smoke but they are probably going to be OK. We have firefighters with those people," Mr Hawkins said.