One of the suspects - a 33-year-old unidentified man - was killed when off-duty police who were nearby returned fire.
The news site NJ.com cited Onofri as describing a chaotic and confusing scene, as police were swamped with 911 calls reporting a shooting inside the venue.
A third unidentified suspect is hospitalized in critical condition.
"And everybody was running, and one cop ran in the middle of the street and shot at this guy", Forchion is heard saying on the video of the person not moving in the street.
Onofri said the shooting appeared to be related to neighbourhood gang violence, and was not being considered a terrorist attack. Police had been trying to shut the festival down. "Twenty individuals were treated for a variety of gunshot wounds as well as other injuries". One of the suspects was killed.
Onofri said 17 of those injured had gunshot wounds. The festival entrances had no metal detectors, he said.More news: USGA CEO admits US Open course was 'too tough'
"I had a walkie-talkie and said, 'All hell just broke loose here, '" said Bruce Toth, who has been curating the free, public art event for the past 12 years and says he was 20 feet away from the gunfire. "It was pretty gnarly", Nicolo said.
Trenton police Lt. Darren Zappley says multiple people have been shot and were taken to the hospital, where some are in surgery. He is in extremely critical condition according to Onofri, reports CNN. Authorities say Wells was just released on parole in 2018 for a felony conviction. Some of what she says is hard to make out.
Festival organizers said the remainder of the event, which was to stretch into Sunday afternoon, would be canceled. More than 900 artists submit their work for display, and attendance surges into the thousands, about 13,000 in 2011, for example, according to the event's Facebook page.
Forchion told New Jersey 101.5 he was also at this weekend's event, and said he was standing mere feet from where the shooting started.
Police found multiple weapons at the scene of the festival, which went on for 24-hours but was ended after the violence.
Outside the event space in Trenton Sunday morning, tables with food and drinks were abandoned and trash cans turned over, with garbage littered around the area as investigators remained on the scene. There was little sign of the shooting outside the building. "Our honest, heartfelt sympathies are with those who were injured", festival organizers said on Facebook.
The Mercer County's Prosecutors Office Homicide Task Force is taking over the investigation as there was an officer-involved shooting, officials said.