The Kincade Fire in Sonoma County grew overnight to 21,900 acres and containment was at 5 percent as of 7:35 a.m., Cal Fire officials said.
The fire started northeast of Geyserville about 9:30 p.m. Wednesday, Cal Fire said.
No injuries have been reported, but 49 structures have been destroyed.
Two thousand people have been evacuated from the area.
All roads east of state Highway 101 in the Geyserville area are closed.