Wildfires break out across California, threatening thousands of homes

Wildfires broke out near Los Angeles, California, as temperatures spiked and humidity levels dropped during a statewide heat wave.

A huge forest fire that prompted evacuations north of Los Angeles was just 12 per cent contained on Thursday. It had charred 17 square miles (44.5 square kilometers) of brush and trees, threatening more than 5,400 homes.

Cooler overnight temperatures helped firefighters increase containment of the fire.

However, Friday's forecast is for hot, dry weather, making for dangerous fire conditions because of possible gusty winds.

The Ranch Fire burns over a residential area in Azusa, California (AP)

California's heat wave was expected to last through the weekend, bringing triple-digit temperatures and extreme fire danger to many parts of the state.

A helicopter prepares to drop water on a fire in California (AP)

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

Firefighters battled the blaze through the night (REUTERS)

Another blaze blackened foothills above the Los Angeles suburb of Azusa. It ripped through nearly 4 square miles (10 square kilometers) of brush and was moving away from homes, but some evacuations were ordered.

Firefighters work to extinguish hotspots (AFP via Getty Images)

A third blaze came dangerously close to a neighbourhood in the city of Corona, east of Los Angeles, before fire crews controlled it.