An airplane drops fire retardant while battling the Wilson Fire near Mount Wilson in the Angeles National Forest in Los Angeles, California, US, October 17, 2017. [Photo/Agencies]

The wildfires have, by Tuesday, burned a combined number of 210,000 acres of land across the state, the California Department of Forestry and Fire Protection (CAL FIRE) said in a press release.

The wildfires killed 42 people, including a firefighter who died in a vehicle rollover in combating the fires, the first death toll from the rank of firefighters in more than a week of fight against the wildland fires, it said.

Nearly 10,000 firefighters continued battling 13 large wildfires burning in the state, and cooler temperatures and increased humidity overnight have aided firefighters in their efforts, CAL FIRE said.

Light rain forecast for northern California, the major impact areas of the most devastating wildfires in the state, will help in the containment progress, it added.

More than 90 percent of the fires in Sonoma County, the worst hit area in the ongoing disaster in California, where 19 of the 42 deaths were recorded, has been brought under controlled, according to CAL FIRE estimates.

Full containment, which means the fires will no longer be able to spread, is expected Friday for Sonoma County.

Evacuation orders have been lifted in many counties of northern California, including Napa County, another hardest-hit area, and residents were gradually allowed to go back home for their rebuilding efforts.

California, with a summer warm temperature and low humidity, is vulnerable to forest fires. From 2006 to the end of 2016, an average of 8,317 wildfires took place in the state and burn more than 2,300 acres every year, statistics show.