The "largest [wildfire] in the history" of Los Angeles has forced hundreds to evacuate, the US city's mayor said.

Mayor Eric Garcetti told reporters on Saturday that the blaze, which broke out on Friday and lit up the hills surrounding the northern suburb of Burbank overnight, had already burned 5,000 acres (2,000 hectares).

More than 700 homes were evacuated in a north Los Angeles neighbourhood and nearby areas, officials said.

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Authorities warned of erratic winds that could force them to widen the evacuation zone, after the fire destroyed one house in Los Angeles on Saturday.

"Other than that, no loss of any property," Garcetti said at a news conference. "That is a pretty amazing thing."

Local media later reported that two additional homes had been burned.

The fire was only 10 percent contained with more than 500 firefighters battling it.

The blaze in thick brush that has not burned in decades was slowly creeping down a rugged hillside on Saturday towards houses, with temperatures in the area approaching 38 degrees Celsius, the Los Angeles Fire Department said in an alert.

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.

Video posted online by local media showed the fire burning along a major highway as it broke out on Friday, with smoke hovering over the roadway as cars passed by flames a few dozen feet away. Officials quickly closed a stretch of the freeway.

On the fire line of #LaTunaFire #LAFD continuing full ops through the night to include @LAFDAirOps 📷Peter Sanders pic.twitter.com/AcMOcOEvw0 — LAFD Talk (@LAFDtalk) September 2, 2017

California Governor Jerry Brown issued an emergency declaration on Friday to free up additional resources to battle the blaze.

Wildfires in the western US have burned more than 7.1 million acres (2.9 million hectares) since the beginning of the year, about 50 percent more than during the same time period in 2016, according to the National Interagency Fire Center.