Police calmed the crowd after one man, who suffered a heart attack during the event, and four others with non-life-threatening injuries were taken to area hospitals. The remaining injured were treated at the scene.
The concert was delayed by about 10 minutes, Reuters reports.
One witness told the AP, "There were fights and a lot of pushing and shoving."
The two-day, multi-artist concert, sponsored by a local radio station, will continue today as planned.