California Gov Jerry Brown declared the state of emergency as firefighters in the state's north battled the rapidly spreading wildfires, that have spread to tens of thousands of acres north and east of San Francisco.
Brown said the declaration would speed up the clearing of debris after the fires and waive fees for people needing to replace official documents that were lost in the disaster.
An evacuation was ordered for Middleton, a town of about 1,500 residents located about 50 miles north of San Francisco.
One thousand firefighters in northern California were battling a fast-moving wildfire early today that had razed buildings, forced thousands to flee, and hospitalised four firefighters with second-degree burns.
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The so-called Valley Fire in Lake County, northwest of Sacramento, erupted yesterday afternoon and rapidly chewed through brush and trees parched from several years of drought, according to the California Department of Forestry and Fire Protection (Cal Fire).
Entire towns as well as residents along a 35-mile stretch of highway were ordered to evacuate.
The fire destroyed homes and buildings as it burned through the town of Middletown, where authorities told NBC News that fire hydrants had run dry.
The blaze was heading in a south-eastern direction toward Aetna Springs, Cal Fire spokesman David Shew said.
Shew said the wildfire picked up speed early Sunday morning as wind blew in from a westerly direction.
He said the fire will rank as one of the worst he's seen in terms of devastation during his 28 years with Cal Fire.