Members of the New York Police Department (NYPD) bomb squad are investigating the cause of an explosion in Central Park on Sunday that nearly blew a man's leg off, police told CNN.

Preliminary investigation suggests the explosion was an "experiment with fireworks or homemade explosives," NYPD Deputy Chief John O'Connell was quoted as having said at a news conference Sunday afternoon.

"We do not have any evidence of a constructed device or commercial-grade fireworks," he said, stressing, "There are no specific or credible threats directed at New York for July Fourth."

The victim of Sunday's incident, an 18-year-old tourist from northern Virginia, and two friends jumped off a rock in the park shortly before 11:00 a.m. local time, O'Connell said. As they did, an explosion occurred, injuring one of them.

The victim was transported to Bellevue Hospital in serious but stable condition for surgery. The victim and his two friends are not considered suspects, O'Connell said, according to CNN.

Forensic evidence indicates the explosive was not meant to go off from someone stepping on it, suggesting the work of an amateur hobbyist, said NYPD bomb squad commanding officer Mark Torre.

Witnesses said the sound of the blast rippled through the park like a "cannon," sending birds flying off trees.

Law enforcement sources told CNN the blast left behind some kind of homemade explosive material, which was being tested at a bomb lab.

The United States, as many other countries around the world, has been dealing with the phenomenon of radicalization, and American authorities over the past year or so have arrested and charged several people of supporting the Islamic State (ISIS) jihadist group.

In June, 22-year-old Nicholas Michael Teausant of California was sentenced to 12 years in prison for seeking to travel to Syria to join ISIS.

Teausant, a convert to Islam, had pleaded guilty in December to a charge of attempting to provide material support or resources to a terror group. He was arrested in March 2014 near the Canadian border, while en route to Syria to join the terror network.

He allegedly told the FBI under interrogation that he wanted to go to Syria in the hope of becoming famous and "being on every news station in the world."