The crash, involving at least five vehicles, was reported at about 5:35 a.m. near Magnolia Boulevard, right before the Ventura Freeway interchange, according to the California Highway Patrol.
There was no immediate word on injuries in the crash, officials said.
All but one lane was shut down at Magnolia Boulevard for over an hour as rescue crews and law enforcement officials investigated the scene.
The crash temporarily snarled traffic for miles during the early morning commute.
All lanes were back open by 7:30 a.m.