Interstate 5 was closed in both directions about 10 miles north of Castaic at Templin Highway in Los Angeles County on Saturday afternoon because of a brush fire, according to Caltrans.
Motorists were urged to use an alternate route as the Route Fire burns.
Angeles National Forest reported on Twitter at about 5:20 p.m. that the fire was 75 acres, had jumped the interstate and was 0 percent contained.
Shortly after 6 p.m., the fire had grown to 140 acres with an unknown number of structures threatened. By 6:30 p.m., the fire was reported to have spread to 392 acres.
Around 7:15 p.m., Angeles National Forest said "we are making good progress on the fire due to an aggressive aerial and ground attack" on Twitter, and noted that helicopters would be making fire retardant drops throughout the evening.
Two firefighters had burn injuries, according to Angeles National Forest.