More than 14,000 fire-fighters are battling 585 fires that have now burnt nearly one million acres (400,000 ha).
Forecast high winds are threatening to drive flames into more populated areas as foul air blankets the state.
At least six people have died and thousands have evacuated.
Most of the destruction has been caused by three large fires complexes in mountainous and wooded rural areas.
On Saturday Governor Gavin Newsom said the SCU Lightening Complex fire south and east of San Francisco is the third-largest in California's history.
Video tweeted by the governor showed burnt tree stumps against the reddened fumes-filled sky and plumes of white smoke rising from ash-laden ground.
An evacuation order on Saturday extended to thousands of people in the Bay area near San Jose and warned others to be prepared to abandon their homes at short notice.
More about:
