LOS ANGELES (AP) — Bone-dry vegetation fuelled three wildfires near Los Angeles amid warnings today that the risk of new blazes erupting was high as temperatures spike and humidity levels drop during a statewide heat wave.

A huge forest fire that prompted evacuations north of Los Angeles was just 12 per cent contained and after threatening more than 5,400 homes, it had charred more than 18 square miles (46.6 square kilometres) of brush and trees.

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

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 nearly 4 square miles (10 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 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 (202 hectares) before firefighters stopped its forward spread.