Some structures may be threatened by the flames.
The Route Fire was reported just before 4 p.m. along the 5 Freeway near Templin Highway.
The CHP closed the southbound 5 at Vista del Lago Road and the northbound 5 at Templin Highway.
The fire was first estimated at 5 acres but spread to at least 50 in less than two hours. It was then estimated at 140 acres after it jumped the freeway, and then spread to 392 acres.
As of 6:30 p.m. the fire remained 0% contained.
Two firefighters were being treated for burn injuries.
DEVELOPING: This story will be updated.