(CNN)A group of people threw glass bottles and other debris at New York City Police Department vehicles early Sunday morning in Harlem after police responded to a "shot spotter activation," according to NYPD Sgt. Mary Frances O'Donnell.
NYPD cars hit with glass bottles and other debris in Harlem after responding to report of gunfire detected
"Shot spotters" are meters placed across New York City that detect the sound of gunshots. After determining the approximate location of the shots, the meters relay information to 911 operators, who initiate a police response, an NYPD spokesman said.
O'Donnell said that while a preliminary investigation of the shots fired resulted in the discovery of several spent shell casings and two fired bullets, no injuries were reported as a result of the shots.
Police tried to disperse a crowd of approximately 500 people who were gathered in the vicinity of where NYPD officers had responded, but "several individuals threw glass bottles and objects at the officers," O'Donnell said.
"Additional police units were requested to the scene and verbal orders to disperse were issued to the large group. The officers' attempts to move towards the crowd were once again met by bottles and debris thrown at them," according to O'Donnell.