Officers are reviewing footage from the event and speaking with several witnesses.
Authorities reported that three of the victims were in critical condition, while the fourth was in stable condition, News.Az reports, citing Fox News.
All were taken to a hospital for treatment.
The incident occurred shortly before 7:30 p.m. near the intersection of Union Street S and Corban Avenue during the city's annual Tree Lighting Ceremony.
Police, Concord Fire and Cabarrus County EMS personnel were already at the event and responded immediately with medical aid and evacuation efforts.
The remainder of the event was canceled after the shooting.
The city said visitors should leave the area and drivers should seek alternate routes.
Concord Police said the incident remains under investigation.
