BONE-DRY VEGETATION fuelled three wildfires near Los Angeles amid warnings Friday that the risk of new blazes erupting was high, as temperatures spike and humidity levels drop during a statewide heatwave.

A huge forest fire that prompted evacuations north of Los Angeles was just 12% contained, and after threatening more than 5,400 homes, it had charred more than 18 square miles of brush and trees.

Cooler overnight temperatures helped firefighters increase containment, but the forecast was for hot, dry weather with dangerous fire conditions because of possible gusty winds, officials said.

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 nearly four square miles of brush on Thursday and was moving away from homes. Evacuation orders issued to residents were lifted early this morning.

Another blaze came dangerously close to a neighbourhood 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 500 acres before firefighters stopped its forward spread.