Angelo Nicolo was attending the event with his brother. He told US media that they heard loud popping sounds and 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,” Mr Nicolo said.
This was the 12th year of the Trenton Art All Night Festival, an event that raises money for local artists. It began on Saturday afternoon and was due to run until Sunday afternoon, but has now been cancelled.
The organisers said, on their Facebook page, they were “shocked” and “deeply saddened” by what had happened.