A total of 16 of the 20 injured were treated for gunshot wounds and four of those hurt – among them a 13-year-old boy – were in a critical condition, according to Mercer County Prosecutor Angelo Onofri.
Mr Onofri said the shooting broke out in the early hours of Sunday, at the event in the city of Trenton. Up to 1,000 people were present when the shooting began.
“It’s a massive crime scene,” he added. Angelo Nicolo told ABC News that he and his brother were at the event when they heard popping sounds. He said people started running down the street.
“I saw two police officers escort a guy that got shot in the leg. They bandaged him up and whisked him away,” he said.
Local television stations showed numerous police vehicles at the scene. The Trentonian newspaper said that the venue for the festival was strewn with broken glass and other debris. The event began Saturday afternoon and was scheduled to conclude Sunday afternoon.
“This is truly a tragedy for Trenton,” Trenton Mayor Eric Jackson said in a statement.
Officials said they had identified at least two suspects in the shooting. One, a 33-year-old man, was pronounced dead while the other was taken into police custody. Mr Onofri said that authorities are investigating if the suspect was shot and killed by someone else, or police. Trenton police at the scene told local media that officers engaged with at least one gunman.
The event, Art All Night, was organised as an opportunity for people to see and experience a wide range of works of art. Its organisers posted on Facebook expressing regret that they had to cancel the festival and offered their condolences to those caught up in the shooting.
“It’s with great regret that we announce that the remainder of Art All Night has been cancelled due to a tragic incident that occurred overnight,” it said.
“We’re still processing much of this and we don’t have many answers at this time but please know that our staff, our volunteers, our artists and musicians all seem to be healthy and accounted for. Our sincere, heartfelt sympathies are with those who were injured.”