This photo ? released on October 18, 2017, by Airbus DS and taken by Constellation DMC satellite ? shows wildfires in California, with the black zones highlighting areas devastated by the fire, October 15, 2017. AFP/Handout via Airbus DS/DMC Constellation/UK-DMC 2

SAN FRANCISCO: The death toll from California's wildfires rose to 42 on Wednesday, the California Department of Forestry and Fire Protection (Cal Fire) said, as rescuers found another body.

The latest victim was found in Sonoma County, the worst-hit part of California's wine-growing region that has been scorched by multiple infernos raging since October 9 but now largely under control.

Cal Fire said almost 10,000 firefighters were still battling 13 major fires, however, with more than 850 square kilometres (325 square miles) burned across the state.

More than 22,000 people have still not been able to return home, down from 75,000 a few days ago.

"Cooler temperatures and increased humidity overnight have aided firefighters in their efforts," Cal Fire said in a statement.

"Weather conditions this week will continue to help in the containment progress. In fact, light rain in northern California is forecast for Thursday night," it added.

Around 5,700 homes and businesses have been destroyed by the fires, the deadliest in California's history.