Fanned by gusting winds, wildfires are raging in densely populated Southern California for a fourth day with a new blaze north of San Diego exploding in size in just a few hours, and dangerous conditions forecast until Sunday.

The blazes destroyed hundreds of houses and forced many Los Angeles-area schools to close.

Flames hopscotched over highways and railroad tracks, and residents rushed to evacuate their homes with only minutes' warning.

People feared for the safety of animals from cats to llamas.           

About 200,000 residents were evacuated from their homes at one point, though some are due to return later.

Authorities said the four biggest fires - ranging from Los Angeles up the Pacific coast to Santa Barbara County - were whipped up by the region's notorious westward Santa Ana winds that could reach hurricane strength.

The winds blow in hot and dry from the California desert, and the state Cal Fire agency said gusty winds and extremely low humidity would continue until Sunday.

"Prepare now to ensure if evacuated you and your family are ready to GO!" Cal Fire said on Twitter.

The Thomas Fire northwest of Los Angeles grew to 115,000 acres from 96,000 acres and destroyed 439 buildings, officials said. 

North of San Diego, another blaze called the Lilac Fire grew from 10 acres to 2,500 acres in just a few hours prompting Governor Jerry Brown to declare a state of emergency for San Diego County.

No civilian casualties or fatalities have been reported from the blazes but three firefighters have been  injured, the Los Angeles Fire Department said.