Four firefighters were hospitalised with injuries from fighting a fast-moving wildfire in northern California that expanded yesterday and has forced thousands of people to evacuate their homes, officials said.

The fire, nicknamed the Valley Fire, spread rapidly overnight and had burned about 16,187 hectares as of yesterday morning, the California Department of Forestry and Fire Protection (Cal Fire) said on Twitter. More than 1,000 fire personnel were battling the blaze, which was zero per cent contained yesterday after erupting a day earlier in Lake County, north of San Francisco, Cal Fire said.

Additional evacuations were ordered early yesterday. Local media showed footage of several structures ablaze in Middletown, a small community of ab-out 1,500 residents, one of several that were evacuated.

Four firefighters, who had been dropped off by helicopter, suffered second-degree burns as they built containment lines, said Cal Fire spokesman Daniel Berlant.

The firefighters were airlifted to UC Davis Medical Center in Sacramento, Berlant later said on Twitter.

The hospital declined to comment yesterday on the condition of the firefighters.

About 161 km to the southeast another blaze, the so-called Butte Fire, has destroyed 86 homes and 51 outbuildings in rural Amador and Calaveras counties. The fire is 20 per cent contained and covers more than 26,305 hectares, officials were saying yesterday.

Thousands of residents in the area of the Butte Fire were required to evacuate on Friday, and the blaze threatened more than 6,000 structures, officials said.

More than 3,800 firefighters were working to contain the fire, which erupted on Wednesday near the former gold mining town of Jackson. Flames from a larger blaze, dubbed the Rough Fire which is burning in Kings Canyon National Park in central California, had forced officials to order about 3,500 to evacuate by Friday, said Jim Schwarber, a spokesman for the team handling the blaze. Firefighters on Saturday intentionally set low-intensity fires in a famed grove of giant sequoia trees in Kings Canyon National Park to remove vegetation and protect the grove from the wildfire, Schwarber said. The giant sequoias themselves are naturally flame-resistant, officials said.More than 2,900 firefighters were on the front lines of the blaze on Saturday, with containment listed at 29 per cent, officials said.

Ranking as California’s largest active fire, the Rough has scorched about 52,000 hectares.