The Long Hollow Fire near Dufur in North Central Oregon has grown to 34,000 acres.
Burnout operations are helping to contain the fire, but also caused it to grow in size.
The fire crossed the Deschutes River and residents in the area have been warned to prepare for evacuation.
Firefighters on the ground are being supported by two Single Engine Air Tankers and three helicopters.
The fire is believed to have been caused by a combine.