A 350-acre wildfire amid blazing hot temperatures forced the evacuation of 300 homes in the hills northeast of Los Angeles today, officials said.

The cause of the fire, which is expected to take two to three days to contain, was under investigation, said Elisa Weaver, a spokeswoman for the city of Sierra Madre, California.

Temperatures in Sierra Madre were expected to climb to an unseasonably hot 37 degrees Celsius today but Ms Weaver said low winds and humidity would help the firefighting effort.

"So far the weather is in our favor," she said, adding that the fire so far had only affected one small storage structure. About 400 firefighters were assigned to the fire, which was about 5 per cent contained early today morning.

Sierra Madre is about 20 miles northeast of downtown Los Angeles.

Late last year, strong winds, high temperatures and parched brush after a record drought were blamed for spreading a series of blazes from Santa Barbara to the Mexican border that destroyed thousands of buildings and drove hundreds of thousands of Californians from their homes.