A firework that exploded and seriously injured the foot of a 19-year-old who stepped on it in Central Park probably was created by someone with a basic knowledge of chemistry, but not designed to intentionally hurt people, police said.

The homemade explosive that went off Sunday probably was designed to “make a large noise, maybe make a flash,” said Lt. Mark Torre, commanding officer of the New York Police Department’s bomb squad. It was like an “explosive experiment” put together by someone with some knowledge of chemistry, he said.

The injured man, who police did not identify, was walking in the park with two friends when he stepped on a rock covering the explosive. He was to undergo surgery to his left foot at a hospital and was in stable condition, fire officials said.

The 11 a.m. blast on the east side of Central Park could be heard for blocks, leaving some with the belief that it was part of a July Fourth celebration.

Investigators don’t believe the man who stepped on the firework or his friends were responsible for creating the explosive and officials asked that anyone with information about it contact the police.

There was no evidence that the explosion was related to terrorism and there were no specific, credible threats on New York over the July Fourth weekend, authorities said.

“We’ve seen a lot of experimentation with homemade fireworks,” said Torre, adding the Central Park explosive may have been designed to go off at an earlier time, even a day before, but for whatever reason did not.

Tourist John Murphy, visiting the city from Connecticut, stayed with the injured man until emergency responders arrived and placed a tourniquet on his leg.

“His left leg was severely damaged, all bone and muscle,” said Murphy.

Mayor Bill de Blasio sent out a tweet reminding people to stay safe around fireworks.

“Fireworks are fun — but let’s leave them to the professionals,” the mayor tweeted.

(AP)