LOS ANGELES • California's biggest wildfire on record raged yesterday as hot and windy conditions challenged thousands of firefighters battling eight major blazes burning out of control across the state.

The Mendocino Complex blaze grew to span about 114,530ha on Monday, when two wildfires merged at the southern tip of the Mendocino National Forest, the California Department of Forestry and Fire Protection said.

It is the largest of eight major fires burning out of control across California, prompting United States President Donald Trump to declare a "major disaster" in the state.

The size of the fire has surpassed that of last year's Thomas Fire, which burned some 114,080ha in Santa Barbara and Ventura counties when it destroyed more than 1,000 structures. The Mendocino Complex has burned 75 homes and forced thousands to be evacuated.

Temperatures could reach 43 deg C in northern California over the next few days, with gusty winds fanning the flames of the Mendocino Complex, a National Weather Service meteorologist said.

Elsewhere in California, evacuations were ordered for cabins in Cleveland National Forest canyons in Orange County on Monday afternoon after a blaze broke out and quickly spread to span 283ha. The Carr Fire, which broke out on July 23, was 47 per cent contained.

Environmental activists and some politicians say the intensity of the state's wildfire season could be linked in part to climate change.

REUTERS