No injuries or structural damage were immediately reported.
According to the Angeles National Forest's Twitter account, the blaze was burning shortly before 1:30 p.m. about 2 miles north of Templin Highway. The California Highway Patrol closed 2 lanes on the 5 Freeway at the scene.
Forest officials also tweeted that Los Angeles County Fire air crews were making good progress suppressing the flames.
Traffic in the area was backed up for nine miles and was expected to cause major delays after two northbound lanes of the freeway were shut down.
Two right lanes are still closed. No estimated time for opening. The traffic backup is 9 miles long with a 70-minute delay. Use other routes such as State Route 14 and allow extra travel time. Updated info at https://t.co/cxZ0jVPIRf https://t.co/xK57lU0tuC— Caltrans District 7 (@CaltransDist7) August 4, 2019
There was no estimated time for reopening them to traffic.
The cause of the fire was unknown.
DEVELOPING: More details will be added to this report as they become available.