Crews are battling the Boone Fire, west of Coalinga.
It sparked Tuesday afternoon off Highway 198 and Boone Lane.
The wind driven flames quickly scorched more than 3,000, but CAL FIRE reports more than 8,500 acres have now burned as of Wednesday morning with no containment.
CAL FIRE says at least three structures are threatened by the flames.
Officials say one firefighter was taken to the hospital, but the extent of their injuries has not been released.
Highway 198 is closed in both directions at Boone Lane.
Fire officials expect crews to remain on the fire for several days.
The cause of the fire is under investigation.