The collision happened around 4 p.m. at the Pasadena Police Department heliport at 2175 Yucca Lane in Altadena.
In a press release, Pasadena police said it was, "an incident where their rotator blades were believed to have touched during a maneuver at the police heliport."
The six injured, five police officers and one civilian, were taken to a hospital for evaluations.
Both OH-58 aircraft sustained extensive damage, police said. One helicopter was on routine assignment to calls for service and the other was assigned to the USC-UCLA game at the Rose Bowl. Each helicopter had a pilot and an observer. Two of the injured were not on board.
It's unclear if the weather may have been a factor in the collision.
The National Transportation Safety Board will conduct an investigation.
The Associated Press contributed to this report.