Around 2:17 p.m., New Jersey State Police say a Hamilton Township, Mercer County police officer observed a shooting in progress in the area of West State Street and Parkside Avenue.
The officer, who was operating an unmarked task force vehicle, followed the suspect vehicle where a gunman fired on the officer, hitting his car.
Police say three men and one woman fled on foot but were later arrested. Officers also recovered several weapons during the investigation.
The officer was not injured in the incident.