Two vehicles, one of them an ambulance, were hit by gunfire in separate freeway shootings that left one man injured, officials said. A 20-year-old man was in stable condition at Los Angeles County Harbor-UCLA Medical Center (search) following one shooting Thursday, officials said.

A bullet grazed the man's head in an apparent gang-related, vehicle-to-vehicle shooting, said sheriff's Deputy Scott Gage. He was not identified.

Four shell casings fired from a .40-caliber handgun were found on the freeway. Authorities were searching for a dark blue Nissan Altima or Honda Civic.

In a separate shooting, an ambulance traveling on Long Beach Freeway (search), also south of downtown, was struck by a bullet. No one was injured.

Authorities continued their investigations of both incidents.