By Sara Puig
Thousands of firefighters are struggling to contain wildfires that have forced the evacuation of thousands of homes and burned more than 121,000 acres of land.
The number of fires had been reduce from 21 to 18, but a new fire that erupted in Ventura county on Sunday and was quickly dubbed the Chorro fire.
The biggest fire, the Rocky Fire, was sweeping through Colusa, Lake and Yolo counties north of Sacramento, the state capital.
More than 13,000 people have been forced to flee homes threatened by Rocky, CALFIRE spokeswoman Alisha Herring said.
She said 12 percent of the fire was under control and it has burned through more than 60,000 acres, destroying 50 structures, about half of them homes, and threatened 6,000 more.
A total of 121,000 acres of land have burned so far, according to state figures.
Governor Jerry Brown's office said around 9,600 people were battling the fires early Sunday.
Dry lightning strikes sparked most of the fires, but the causes of the others remained unknown. Authorities said they did not suspect foul play.
Thousands of lightning bolts since Thursday caused hundreds of smaller fires throughout the state, but most of the blazes were concentrated in the north, California fire chiefs said.
"Our firefighters have been working extensively throughout the last two weeks, working hard to contain these fires. The weather has not been so kind," CALFIRE spokeswoman Lynnette Round told AFP.
"The dry, warm windy conditions then the dry lightning hitting, it just fuels those fires."
Brown's office said neighbouring Nevada and Colorado had also committed resources to battle the blazes.
Stretches of Highway 20 were closed in both directions, spelling weekend travel misery for motorists.
But late Sunday, CALFIRE had some better news on other fronts: the Lowell fire, in Nevada county, was 85 percent contained; the Wragg fire in Napa was 95 percent contained; and the Fern fire in Shasta county was 60 percent contained.
Witnesses described dramatic scenes as thick smoke from the giant fire turned day into night and flames swallowed up large tracts of woodland and forest.
Vehicles were left to the flames, abandoned and burnt-out.
Brown declared a state of emergency on Friday and called in the California National Guard.
Firefighter Dave Ruhl, 38, from South Dakota, was killed Thursday while fighting the Frog Fire in the Modoc National Forest outside Alturas.
"California's severe drought and extreme weather have turned much of the state into a tinderbox," Brown said in a statement.
"Our courageous firefighters are on the front lines and we'll do everything we can to help them."
"Firefighter Ruhl will be remembered for his service and bravery and we extend our deepest condolences to his family, friends and colleagues with the US Forest Service," Brown said in a separate statement.
Wildfires are a fact of life in much of California, but were far worse than usual this year because of bone-dry conditions, with the state gripped by a fourth year of record drought.