Three vehicles were involved in the crash, which was reported shortly after 5:30 a.m. near Firestone Boulevard, according to the California Highway Patrol. The number of people injured and their conditions were not immediately known.
Firefighters responded to the scene and extinguished a blaze that engulfed a minivan involved in the collision.
Four lanes were reopened just before 6:30 a.m., but traffic remained snarled from the crash site to the 91 Freeway.
The cause of the incident was unknown.
DEVELOPING: More details will be added to this report as they become available.