Twin blazes in northern California have become the largest wildfire in the state’s history.

The fires had scorched 455 square miles by Tuesday — nearly the size of the city of Los Angeles.

The Mendocino Complex fire north of San Francisco was still growing this week as it broke the record set eight months ago.

In December, the Thomas Fire killed two people, burned 440 square miles and destroyed more than 1,000 buildings in Southern California.

The Mendocino Complex, which is 34% contained, has been less destructive to property than some of the other wildfires in the state because it is mostly raging in remote areas.

But officials say it threatens 11,300 buildings and some new evacuations were ordered over the weekend as the flames spread.

Hotter weather attributed to climate change is drying out vegetation, creating more intense fires that spread quickly from rural areas to city subdivisions, climate and fire experts say.

California Wildfires
The size of the fires surpasses a blaze last December in southern California (Jae C Hong/AP)

But they also blame cities and towns that are expanding housing into previously undeveloped areas.

More than 14,000 firefighters are battling more than a dozen major blazes throughout California, state Department of Forestry and Fire Protection spokesman Scott McLean said.

“I can remember a couple of years ago when we saw 10 to 12,000 firefighters in the states of California, Oregon and Washington and never the 14,000 we see now,” he said.

Crews made progress over the weekend against one of the two blazes in the Mendocino Complex with help from water-dropping aircraft, Cal Fire operations chief Charlie Blankenheim said in a video on Facebook.

But the other one is growing after spreading into the Mendocino National Forest and then spreading south to Colusa County.

Meanwhile, a new fire erupted south of Los Angeles in Orange County on Monday and quickly spread through the chaparral-covered ridges of the Cleveland National Forest. Campgrounds and homes in Holy Jim Canyon were ordered evacuated. The fire sent up an enormous pillar of smoke and ash.

Crews also gained ground against another Northern California wildfire that has destroyed more than 1,000 homes in and around the city of Redding. It was nearly halfway contained, Cal Fire said.

That wildfire about 225 miles north of San Francisco started more than two weeks ago by sparks from the steel wheel of a towed-trailer’s flat tyre. It killed two firefighters and four residents and displaced more than 38,000 people.