UPDATE: Investigators Test Explosive That Blew Off Part of Man's Leg in Central Park

An 18-year-old Virginia man had to have part of his leg amputated after he was severely injured in a small explosion in Central Park that investigators suspect was caused by a homemade "experiment" left behind by an amateur or hobbyist.

The explosion happened around 11 a.m. inside the park at East 68th Street and Fifth Avenue, according to the FDNY.

Investigators stressed that there was no evidence that the explosion was a terrorist act.

"There are no specific or credible threats directed at New York or the July Fourth celebrations," said Inspector John O'Connell, the head of the NYPD's counterterrorism unit.

Relatives identified the injured man as 18-year-old Connor Golden of Fairfax County, Virginia. Terry and Roberta Golden, the teen's grandparents, told News4 in Washington that doctors had to amputate his injured leg below the knee. An official said he underwent the surgery at Bellevue Hospital.

Golden is an Eagle Scout, musician and honor student at University of Miami in Coral Gables, Florida, the grandparents said. He is turning 19 next Sunday.

"I would guess that he would love to continue at the University of Miami and sports," said Roberta Golden. "I have no idea how he would go about it and ironically his birthday is next Sunday and he wanted a long skateboard. Everybody in Miami has them."

Two of Golden's friends told police they were visiting the city from Virginia and denied they were playing with fireworks. The NYPD bomb squad was investigating to determine exactly what material caused the injury.

Breaking. Loud boom in Central Park. Man suffers major injury to leg. #nbc4ny pic.twitter.com/qI6reOjvuN — Lori Bordonaro (@LoriB_NY) July 3, 2016

Police said during a late afternoon news conference that they believe the victim and his two friends had nothing to do with the explosive material. They refrained from referring to it as a device. The victim jumped off a rock and his left foot landed on the homemade material, causing it to explode, they said.

"It was almost like it was hidden," O'Connell said. "But it wasn’t where someone ordinarily would’ve stepped."

The NYPD cordoned off a two- to three-block area of the park near the blast site. Bomb-sniffing dogs were sent into the area to search for an other explosives.

Lt. Mark Torre of the NYPD bomb squad said the material didn't appear to have been "shock-sensitive." He said there was no evidence that it was meant to explode if stepped upon.

"We’ve seen a lot of experimentation with homemade fireworks," he said. "Their goal is to make a loud noise, maybe make a flash."

Mayor de Blasio took to Twitter on Sunday night and said the explosion appeared to be an "isolated incident, unrelated to terrorism."

"Central Park, both statistically and by reputation, is one of the safest patches of land in any big city in America," he wrote.

De Blasio said there was no threat directed at New York City for the Fourth of July celebrations and encouraged people to come out and enjoy the park.

Tenzin Ratling, 46, a photographer who sells his work most days on the perimeter of the park, said that he heard the blast and initially thought it was some type of test for a Fourth of July fireworks display.

"But then many police arrived and I thought that a bad thing happened," he said.