California wildfires: Biggest ever blaze in worst ever season

Firefighters are continuing to battle a Californian wildfire which has been declared the biggest ever recorded, in what could be the worst Californian fire season in history.

Almost 4000 firefighters are struggling against rugged terrain, high winds and an August heat wave up to 32C to slow the spread of the inferno that exploded to more than 725 square miles in just 11 days.

In total, 14,000 firefighters were battling blazes across California, which is seeing earlier, longer and more destructive wildfire seasons because of drought, warmer weather attributed to climate change, and the building of homes deeper into the forests.

The biggest blaze, near the community of Clearlake, about 160km north of San Francisco, spread fast.

The flames were burning in mostly remote areas, and no deaths or serious injuries have been reported.

But at least 75 homes have been lost, and thousands of people living near Clearlake have been forced to flee.

The blaze, dubbed the Mendocino Complex, was reported to be only 20 percent contained.

Its rapid growth to an area the size of Los Angeles at the same time firefighters were battling more than a dozen other major blazes around the state fanned fears that 2018 could become the worst wildfire season in California history.

Australian teams have gone to help battle the blazes.

"For whatever reason, fires are burning much more intensely, much more quickly than they were before," said Mark A. Hartwig, president of the California Fire Chiefs Association.

The area has few roads that can serve as firebreaks, and firefighters instead fell back to natural barriers like streams or used bulldozers to cut fire lines.

But the flames were moving so fast in spots that they blew past fire lines, forcing firefighters to retreat, said Battalion Chief Jonathan Cox of the state Department of Forestry and Fire Protection, or Cal Fire.

"Cal Fire is really an urban firefighter service in the woods," said Arizona State University professor Stephen Pyne, a wildfire management expert.

The Mendocino Complex is actually two blazes burning so close together that authorities are attacking them as one.

The fires started July 27 within an hour of each other and about 24km apart.

As of Tuesday, they were separated by just a few miles. Officials have not determined the cause of either one.

In becoming the biggest fire in California history, the Mendocino Complex fire broke a record set just eight months ago.

A blaze in Southern California in December killed two people, burned 708 square km and destroyed more than 1,000 buildings.

Crews also gained ground this week against another Northern California wildfire, one that destroyed more than 1,000 homes in and around the city of Redding and was blamed for at least six deaths.

California's firefighting costs have more than tripled from $242 million in the 2013 fiscal year to $773 million in the 2018 fiscal year that ended June 30, according to Cal Fire.

"We're in uncharted territory," Gov. Jerry Brown warned last week.

"Since civilization emerged 10,000 years ago, we haven't had this kind of heat condition, and it's going to continue getting worse. That's the way it is."