A wildfire raging through the foothills and canyons of northern California's coastal mountains more than doubled in size as it roared into its fifth day on Sunday, leaving two dozen homes in charred ruins and displacing thousands of residents.

The blaze, which has scorched about 22,000ha east of Lower Lake, a town 180km north of San Francisco, was the fiercest of 20 large fires being battled by 9,000 firefighters across the state, officials said.

The so-called Rocky Fire that erupted in Lake County last Wednesday has proved the most destructive. "This is a very fast-moving wildfire," said Mr Daniel Berlant, a spokesman for the California Department of Forestry and Fire Prevention, or Cal Fire.

Some 8,000ha of scrub and brush ravaged by the fire over a five-hour period last Saturday night represented "unprecedented growth in that short amount of time", he added. By Sunday evening, the blaze had blackened another 2,800ha along the rugged eastern flanks of California's Northern Coast Ranges, officials said.

After destroying 24 homes and 26 outbuildings last week, the fire continued to threaten an estimated 6,300 structures and has forced the closure of parts of two state highways, Cal Fire said. Over 12,000 people have received mandatory evacuation orders or advisories.

REUTERS