
California Governor Jerry Brown has declared a state of emergency as a wildfire that forced 21,000 people from their homes continues to rage south of Los Angeles.

Brown issued the declaration on Thursday for Orange and Riverside counties because of the Holy Fire in the Cleveland National Forest, which is threatening thousands of homes.

The fire near Lake Elsinore is devouring brushy foothills, ridgetops and canyons. It's blackened 16 square miles and is only 5 per cent contained.

On Thursday, flames came within yards of some homes. Twelve structures have been confirmed destroyed in the fire so far - and elsewhere the Carr Fire has destroyed nearly 1,100 homes.

A firefighter works to protect homes as flames arrive during the Holy Fire in Lake Elsinore, California on Thursday

A man watches as fire races down a hillside towards his home as the Holy Fire burns in Lake Elsinore, California on Thursday

A firefighting helicopter makes a water drop as the Holy Fire burns near homes on Thursday in Lake Elsinore, California

This map shows the locations of the major fires now burning across the state of California, with the Holy Fire in the south

A firefighting helicopter drops water to protect homes during the Holy Fire in Lake Elsinore, California on Thursday

The burn area of the Holy Fire in the Cleveland National Forest on the county line between Orange and Riverside is seen above

Early on Friday, more than 1,200 firefighters were fighting the blaze, building barriers and constructing containment lines to slow the approaching wildfire.

More than 21,000 people have been evacuated in and around Lake Elsinore, where furious flames and billowing smoke rose into the sky at the edge of the city of 60,000 as the Holy Fire burned nearby in the Santa Ana Mountains.

'It feels like a war zone,' Ana Tran told the Los Angeles Times as ash and flame retardant fell on her neighborhood.

The fire was being fueled by dry brush covering steep terrain and stoked by erratic wind gusts during the night, said Thanh Nguyen, a spokesman for the incident said.

'Strong down drafts is making the fire move aggressively downhill,' said Nguyen, noting that firefighters were working to build barriers and containment lines to protect more than 2,000 homes at risk from the fire.

Firefighters set a backburn to fight the Holy Fire as it burns in the Cleveland National Forest along a hillside at Temescal Valley

A CalFire firefighter (far left wearing yellow) oversees an inmate fire crew (wearing orange) as they clear brush and put out hotspots to protect an elementary school that almost caught fire at the Holy Fire in Lake Elsinore, California on Thursday

An inmate fire crew clears brush and puts out hotspots to protect an elementary school that almost caught fire at the Holy Fire in Lake Elsinore, California, southeast of Los Angeles, on Thursday

Three firefighters suffered minor injuries battling the blaze that has consumed more than 10,200 acres since it began on Monday, fire officials said.

Forrest Gordon Clark, 51, is charged with intentionally setting the Holy Fire and is scheduled for arraignment on Friday

Arson suspect Forrest Gordon Clark, 51, is charged with intentionally setting the Holy Fire and is scheduled for arraignment on Friday.

Clark is being held pending bail of $1million. He faces a maximum sentence of life in prison if convicted.

The Holy Fire was one of several fires burning in California that have displaced tens of thousands of people.

Wildfires across the state and region could be further stoked by strong gusts, low humidity and hot weather on Friday and Saturday, forecasters warned.

In Northern California, a mechanic helping to fight the Carr Fire burning around Redding was killed in a traffic collision on Thursday, bringing the death toll from that blaze to eight, the California Department of Forestry and Fire Protection said.

A general view of damage caused by the Carr Fire near Redding, California is seen in the photo on Thursday

Damage from the Mendocino Complex Fire is seen on Tuesday in Spring Valley, California. The raging Mendocino Complex fire comprising twin blazes in northern California has now ravaged more than 477 square miles

The 279-square-mile Carr Fire had already killed two other firefighters, a utility worker along with three members of one family, and has destroyed nearly 1,100 homes.

It was 49 per cent contained with firefighters struggling in steep terrain to control the blaze, CalFire said.

More than 4,000 firefighters are battling the Mendocino Complex Fire, which has burned 477 square miles in three counties north of San Francisco, CalFire said.

Two firefighters were injured and 119 homes destroyed by that fire, which now ranks as the largest fire on record in the state.