The fire was reported shortly after 1 p.m. in the 2800 block of Madera Road, according to the Ventura County Fire Department.
By 2 p.m., the blaze had grown to about 10 acres but officials said firefighters were making "good progress" on containment.
The blaze, dubbed the Madera Fire, was described as "pushing quickly" toward the highway. All westbound lanes are closed from Madera Road to Collins Drive, but one lane was expected to be open soon.
The cause of the fire has not been determined.