The crowd was peaceful until around 8:15 pm. An illegal sideshow involving vehicles and motorbikes occurred near Grand Avenue and Bellevue Avenue on Wednesday local time, the Oakland Police Department said in a press statement Thursday.

During the side show, someone walked on the hood of the car, causing the occupants to come out and attack the person. Then there was the shooting, Oakland Police Department Chief Floyd Mitchell said at a news conference Thursday afternoon.

The Oakland Fire Department said it transported at least four gunmen to local hospitals.

Police also took some victims to nearby hospitals. Other victims were self-transported.