The incident happened about 1 a.m. on the interstate, near Alondra Boulevard, according to the California Highway Patrol.
The condition of the injured person was unknown.
Transition roads from the eastbound and westbound 91 Freeway to the northbound 605 were also temporarily closed as an investigation got underway.
It was unclear if anyone was in custody in connection with the shooting.
All lanes and both transition roads were reopened shortly before 6 a.m.