The shooting was reported around 4:11 p.m. near Lorena Street, according to the California Highway Patrol.
One person was killed and another was hospitalized in unknown condition, authorities said.
A white sheet was placed on the passenger side of a Cadillac car that was facing the wrong way next to the center divider. At least one other car at the scene also appeared to have its rear window shattered.
CHP said the agency is searching for three suspects. It's unclear what led up to the shooting.
Authorities warned that the freeway would be closed until further notice while the investigation continued.
City News Service contributed to this report.