The crash was reported shortly before 5 a.m. near the Knott Street exit, according to the California Highway Patrol.
Witnesses said two vehicles were speeding when one crashed into another and hit the center divider, according to the CHP. At least one person got out of a vehicle and was struck by oncoming traffic, authorities said.
Drivers were encouraged to use the Magnolia exit to take Garden Grove Boulevard. It was not clear when all lanes were expected to open.
City News Service contributed to this report.