Firefighters are scrambling to protect thousands of homes from wildfires racing through brush-covered mountains north of Los Angeles that caused hundreds of evacuations and burned a handful of structures.

Bone-dry vegetation is fuelling at least three wildfires amid warnings that the risk of new blazes erupting was high as temperatures spike and humidity levels drop during a statewide heat wave.

The main blaze, dubbed the Lake Fire, has scorched over 4,451 hectares and forced 250 people from their houses since erupting on Wednesday afternoon in the Angeles National Forest.

A huge forest fire that prompted evacuations north of Los Angeles flared up on Friday afternoon, sending up an enormous cloud of smoke as it headed toward the California aqueduct in the Antelope Valley. However, fire crews quickly managed to stop its movement there.

The Lake Fire was just 12% contained, and threatens more than 5,400 homes.

Cooler overnight temperatures helped firefighters increase containment. But the temperature hit 38 Celsius on Friday in the area, and the forecast called for continuing hot, dry weather with dangerous fire conditions because of possible gusty winds.

“The heat, the weather, that's what made this fire go," Nathan Judy of the US Forest Service told KABC-TV.

Record-breaking heat is possible through the weekend, with triple-digit temperatures and unhealthy air predicted for many parts of the state.

Preliminary damage assessments found that at least five buildings burned in the Lake Hughes area north of Los Angeles, but authorities said they believed more had been damaged or destroyed.

There was no containment of a blaze that blackened foothills above the Los Angeles suburb of Azusa. 

It churned through 5.96 square kilometres of brush on Thursday and was moving away from homes. 

Evacuation orders issued to residents were lifted early Friday.

Another blaze came dangerously close to a neighborhood in the city of Corona, east of Los Angeles, before crews controlled it.

And a Northern California fire in the community of Sloughhouse, near Sacramento, burned about 202 hectares before firefighters stopped its forward spread.