One southbound lane of the 5 freeway has been shut down in the Grapevine area after a brush fire in Lebec burned approximately 300 acres on Friday.
Fire officials say the growing fire is threatening to close more of the heavily-traveled stretch of road between Los Angeles and California's Central Valley.
The Bakersfield Californian reports Friday's brush fire near the Tejon Ranch Center is creating extremely heavy smoke.
Kern County Fire Department Engineer Anthony Romero says the fire was reported shortly after 1:45 p.m.
California Highway Patrol officials say one southbound lane has been closed south of Lebec for emergency vehicles and traffic is slowing in the area.
CHP says the fire may have been caused by a big-rig on the side of the highway. The cause remains under investigation.
This story has been updated.