Authorities have evacuated more than 700 homes in the path of the fire

Aaron Funk watches the fire come down the side of the hill behind the home of his parents in the Sun Valley neighbourhood, north of Los Angeles. Photo / AP

More than a thousand firefighters are battling the largest bushfire in Los Angeles history contended with erratic winds, but more moderate temperatures could help contain a blaze that has forced hundreds to evacuate their homes, officials said.

The nearly 2400ha La Tuna Fire, named after the canyon area near the northern edge of Los Angeles where it erupted at the weekend, has destroyed three homes and damaged one.

Authorities had evacuated more than 700 homes in a Los Angeles neighbourhood and in nearby Burbank and Glendale.

The blaze in thick brush that has not burned in decades was slowly creeping down rugged hillsides toward houses and was only 10 per cent contained.

"Our priority is to put firefighters in a position to protect lives and property," Los Angeles Fire Chief Ralph Terrazas said. "There's a lot of fuel out there left to burn."

Temperatures in the area have hovered around 38C in recent days. But the mercury is expected to ease in most of the area throughout today.

Fire officials offered the same estimate on the size of the fire as they did yesterday, but will update the number later in the day.

Los Angeles Mayor Eric Garcetti declared an emergency, ordering "all available resources" deployed to protect residents and property. He said the fire was the largest in the city's history in terms of area.

More than 1000 firefighters from Los Angeles Fire Department and surrounding cities were fighting the blaze, with additional help from state and federal agencies.

Terrazas said at least two firefighters suffered minor heat-related injuries and illnesses. The fire could make air unhealthy to breathe in parts of Los Angeles, the nation's second-largest city, and nearby suburbs, the South Coast Air Quality Management District said in an advisory.

- Reuters, AAP