Twenty people were injured after shots rang out at the Art All Night festival in Trenton, New Jersey, on Sunday. One suspected shooter is believed to be dead.

The incident occurred just before 3 a.m. EDT, when two suspects started opening fire at the crowd gathered for the local art exhibition. According to authorities around 1,000 people were in the arena for the festival. A stampede ensued as panicked revelers ran for cover.

One of the suspects — a 33-year-old unidentified man — was killed when off-duty police who were nearby returned fire. Another suspect, age and identity unknown, was taken into custody.

Sixteen of the twenty people hurt were treated for gunshot wounds. Four of them, including a 13-year-old boy, were rushed to the nearby hospital in critical conditions. The nature of injuries of the other four people is not known.

Angelo Nicolo, who attended the festival, told ABC6 that there was panic all around as soon as people heard gunshots.

"All of a sudden, my brother goes to me, 'You hear that gunfire?' I go, 'It sounds like fireworks,' he said, 'No, that's gunfire'. Next thing you know, we turn around and everybody's running down the street. All hell broke loose,” Nicolo said.

Another festivalgoer Franco Roberts, told local news outlet Trentonian newspaper that a fight ensued between a few people before the gunshots rang out.

“Someone told us they were shutting down the whole building. Then we turned around and saw people squaring up to fight. I saw two punches and then heard several gunshots,” he said.

 The Art All Night festival began Saturday afternoon and was scheduled to continue until the following afternoon.

Mass Shooting 20 people were injured after shots rang out at the Art All Night festival in Trenton, New Jersey. In this photo illustration, a Rock River Arms AR-15 rifle is seen with ammunition in Miami, Florida, Dec. 18, 2012. Photo: Getty Images/ Joe Raedle