An 18-year-old man is seriously hurt in a possible fireworks explosion in Central Park.

Authorities say it happened shortly before 11 a.m. Sunday, inside the park near 68th Street and 5th Avenue.

At a press conference held by the NYPD's bomb squad at the park Sunday night, authorities said the victim and two friends who were with him were not responsible for the explosion.

Police say the man's foot was severed above the ankle in what they believe was a fireworks accident, but the exact cause is still being investigated.

"The explosion could have been an experiment with fireworks or homemade explosives," said Counterterror Chief John O'Connell. "We do not have any evidence of a constructed device or commercial grade fireworks. We believe this could have been put here as some sort of experiment.

"It should also be noted, the victim and his two friends, we do not consider them to be part of the construction of this object," O'Connell added.

One man who was close by when it happened described the scene.

"Everyone in the park, or this end of the park, heard a loud boom," the man said. "It was a loud report. Clearly not a car backfiring, more than a firework. Then heard some young men yelling, went over there on the rocks, and their friend was lying down whose foot was severely injured. And they claim he stepped on something."

Lieutenant Mark Torre, commanding officer of the bomb squad, suggested that the device was made by someone with knowledge of chemistry, but said the result of the explosion seems to have been accidental rather than deliberate.

"There is some forsenic evidence that indicates that it was not meant to go off by somebody stepping on it," Torre said. "It may have not gone off at an earlier time and was just left there."

Authorities say the victim was taken to the hospital.

No one else was hurt.

The bomb squad was still on the scene conducting its investigation as of 6 p.m. Sunday.

Stay with Time Warner Cable News and NY1 for more on this developing story.