At least 20 people were injured on Sunday in a shooting at an all-night arts festival in Trenton, the state capital of New Jersey, that also left one suspect dead, a local prosecutor said.

“Multiple individuals opened fire” inside the festival venue shortly before 3:00 am, Mercer County chief prosecutor Angelo Onofri told reporters.

A 33-year-old man, one of the suspects, was killed, and another was taken into custody, he said.

Among the injured at the Art All-Night Trenton event was a 13-year-old boy in critical condition. Several weapons were recovered at the scene, Onofri said.

The local CBS affiliate said 22 people were wounded, and that four of them were in critical condition. Officials offered no immediate theory as to what prompted the shooting spree, or how it unfolded.

Art All-Night Trenton is an annual event in the city, which is home to 85,000 people and is located about 100 kilometres south of New York.

The event was meant to last 24 hours from 3pm on Saturday.

“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,” organizers said on the event's Facebook page.

“We're still processing much of this and we don't have many answers at this time,” the statement said. “Our sincere, heartfelt sympathies are with those who were injured. “