California governor Jerry Brown declares state of emergency over raging wildfires

California's governor declared a state of emergency on Friday as a string of wildfires raged across the state and a firefighter was killed battling a blaze in drought-parched forest, officials said.

The firefighter, David Ruhl of Rapid City, South Dakota, was on temporary assignment in Northern California, where the brunt of 18 large fires burning across the state have destroyed homes and structures and temporarily displaced hundreds of people, the U.S. Forest Service said.

Ruhl was battling the so-called "Frog Fire," which broke out on Thursday near the town of Adin in the state's northeast, when he was killed on duty, the Forest Service said.

"This loss of life is tragic and heartbreaking,” Forest Supervisor Amanda McAdams said in a statement.

Experts have predicted a long and volatile summer wildfire season in California, in its fourth year of crippling drought.

Governor Jerry Brown's state of emergency will help mobilize additional firefighting and disaster response resources.

"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."

Crews on Friday continued to struggle to gain control of a

rapidly growing wildfire that burned largely unchecked in Northern California's ranch country, destroying three homes and forcing about 500 people to flee.

The blaze has nearly doubled in size from late Thursday morning to scorch some 15,000 acres (60 square km) of California's rural Lake County.

The so-called Rocky Fire started on Wednesday afternoon in the foothills and canyons on the inland flanks of California's northern coastal range, about 110 miles (180 km) north of San Francisco.

Almost 1,000 firefighters were working on the blaze with the help of air tankers and helicopters.

North of Sacramento, a 2,300-acre (9.3-square km) blaze had threatened some 1,800 homes and other structures at its height, but 75 percent of that fire had been contained by Friday morning and evacuation orders were downgraded to advisories, officials said.

In the Southern California county of San Bernardino, east of Los Angeles, officials posted a $75,000 reward on Tuesday for information leading to the arrest and conviction of drone hobbyists whose aircraft have interfered with recent firefighting efforts there.

(This story corrects the first name of governor in the sixth paragraph)

(Editing by Bill Trott)