A 10-year-old boy and his mother suffered graze wounds when a bullet struck the bus they were riding on in South Los Angeles, police said.
The incident was reported at 6:40 p.m. at 42nd Street and Avalon Boulevard.
The boy was treated for a neck wound. His mother was hit in the face with glass and debris.
The wounds were not life-threatening, police said.
It started when two men got in an argument that escalated into gunfire, said LAPD Detective Tommy Thompson.
Up to five rounds were fired.
Detectives, armed with flashlights, collected bullet casings in front of the businesses along Avalon Boulevard.