ANTIOCH (CBS SF) -- A portion of state Highway 4 in Antioch was shut down Friday afternoon to investigate a shooting, according to the California Highway Patrol.

The investigation was underway along eastbound Highway 4 at the Laurel Road exit according to the CHP.

Traffic reportedly began backing up around 1:30 p.m. as officers arrived on scene to investigate but it is not yet clear when the shooting occurred.

The CHP said it was first notified around noon Friday afternoon when a victim arrived at a local hospital with a gunshot wound. The victim was in surgery and the person's condition was unknown.

Eastbound Highway 4 was closed between Laurel Road and Sand Creek Road during the investigation.