Wildfires forced evacuation orders for more than 100,000 people and have left two firefighters seriously injured in Southern California.

Powerful winds across the state prompted power to be cut to hundreds of thousands of homes to prevent new blazes.

Fire spread in size to over 11 square miles after breaking out around dawn in Orange County, LA.

More than 300,000 power customers - estimated at about one million people - were in the dark in the northern part of the state as officials issued warnings for what could be the strongest winds in California this year. 

Firefighting crews that had been at the ready overnight quickly contained small blazes that broke out on Sunday in northern California's Sonoma and Shasta counties. The causes were under investigation.

Officials extended a red flag extreme fire danger warning through to 5pm on Tuesday for the region's eastern and northern mountainous areas.

Scientists have said climate change has made California much drier, meaning trees and other plants are more flammable.

October and November are traditionally the worst months for fires, but already this year 8,600 wildfires in the state have scorched a record 6,400 square miles and destroyed about 9,200 homes, businesses and other buildings. There have been 31 deaths.

The electricity shutdowns marked the fifth time this year that Pacific Gas & Electric, the nation's largest utility, has cut power to customers to reduce the risk of downed or fouled power lines or other equipment that could ignite blazes amid bone-dry weather conditions and gusty winds.

On Sunday, the utility shut off power to 225,000 customers in northern California and later did so for another 136,000 customers in 36 counties.

The conditions could equal those during devastating fires in California's wine country in 2017 and last year's Kincade Fire that devastated Sonoma County north of San Francisco last October, the National Weather Service said.

Fire officials said PG&E transmission lines sparked that fire, which destroyed hundreds of homes and caused nearly 100,000 people to flee.