According to the California Highway Patrol, the crash happened on the eastbound State Route 91 just west of Knott Avenue.

Buena Park, CA – One person was seriously injured in a two-vehicle collision on Highway 91 in Buena Park early Sunday morning.
According to the California Highway Patrol, the crash happened on the eastbound State Route 91 just west of Knott Avenue.
Two vehicles collided in the area in unclear circumstances.
One person suffered severe injuries following the accident.
No more information about the crash was available.
An investigation is ongoing.