The fire near Frazier Park had grown to 2,500 acres just before 4 p.m. Wednesday and was spreading rapidly, the Kern County Fire Department said.
The fire broke out about 1 p.m. on the west side of I-5 just south of Frazier Mountain Park Road and spread to the south and west.
Traffic on I-5 is not affected.
Frazier Mountain Park High School was immediately evacuated and is now being used as a command post for firefighters.
“Strong winds and dry fuels are hampering firefighting efforts, and an evacuation of the Hungry Valley State Park and Piru Creek Campground are in effect,” the KCFD said in a press release at 3:50 p.m.
The fire has spread from the grasslands into chaparral and is now is heavy timber as it burns into the Los Padres National Forest.