Officials from the Orange County Sheriff's Department said the incident happened around 1:25 p.m. near the intersection of Cerritos Avenue and Garza Street.
The victim was taken to a hospital, where he was pronounced dead.
Officials said three suspects in an older model gray Honda fled the scene and were last seen heading eastbound on Cerritos Avenue.
Possible witnesses were being interviewed, sheriff's officials said.
It was unclear what led to the shooting.
Deputies locked down nearby Jonas Salk Elementary School, but that lockdown has since been lifted. The investigation is ongoing.