Man, 37, arrested over US wildfire that threatens over 2,000 homes in northern California

LOS ANGELES (AFP) - US police have arrested a 37-year-old man suspected of starting a wildfire which doubled in size overnight and is threatening over 2,000 homes in northern California, officials said Thursday.

Some 2,800 people have evacuated their homes in the face of the raging King Fire, which has expanded to cover 29,000 hectares.

Wayne Allen Huntsman was arrested Wednesday for arson for allegedly starting the blaze near Pollock Pines, about 225km north-east of San Francisco, a Cal Fire spokesman told a press conference.

Nearly 3,700 firefighters and 300 fire trucks are battling the blaze, one of a dozen raging across California, which is in the third year of its worst drought in decades.

"The fire continued to burn actively throughout the night," said Cal Fire - California Department of Forestry and Fire Protection - explaining the blaze had doubled in size.

"Due to the day's extreme fire behaviour, steep terrain, inaccessibility, variable wind direction and darkness, it was unsafe to approach the north portion of the fire," it said in an online update.

The fire, which is only 5 per cent contained, was likely to grow further, it said.

"There is a high potential for extreme fire behaviour today," it warned.

California is baking in temperatures of nearly 40 deg C and the prolonged drought is devastating California's largely agricultural Central Valley in particular.

The vast western US state often faces fierce fires in the summer and fall, but wildfire season began early this year, with the extreme drought of recent months generating dozens more blazes.

In southern California there was some relief after near-record temperatures over the past week, which triggered outages which left some 7,000 people without power.