A 19-year-old man has been severely injured in an explosion in New York's Central Park.
The tourist from north Virginia has had to have surgery on his foot after stepping on what police believe was a homemade firework.
John O'Connell from the NYPD said three men aged 18 to 20 had jumped off a rock in the park. As they did, an explosion occurred and one of the three was injured.
He said the device could have been an experiment with fireworks or homemade explosives.
"We do not have any evidence of a constructed device or commercial-grade fireworks," he said. "There are no specific, credible threats directed at New York or the July Fourth celebrations."
It is not unknown for people to try and make homemade fireworks around the Fourth of July, O'Connell said, calling such activity "completely unadvisable."
Members of the New York Police Department bomb squad are investigating.