The SCU Lightning Complex of fires burning in seven counties grew to 372,971 acres overnight and was 35 percent contained as of Friday morning, Cal Fire said.
The fires have destroyed 28 structures and are threatening 20,065 more, according to fire officials. Nine structures have been damaged in the blazes.
Five people have been injured, three of them first responders, Cal Fire said.
Cal Fire officials said large columns of smoke will be visible due to planned burns — the smoke is expected to blow eastward toward the main fire area.
Lower humidity expected overnight and into Saturday morning increases the risk of rapid fire growth, especially above 2,000 feet and in the pre-dawn hours.
The fires were sparked by lightning Aug. 16 and are burning in Santa Clara, Alameda, Contra Costa, San Joaquin, Stanislaus, Merced and San Benito counties.