By DAVID CRUZ 

A gas explosion was reported at John F. Kennedy High School in Marble Hill, injuring three people, one critically, according to fire officials.

The evening blast happened just after 8pm in the building’s top floors. Seven employees were working on upgrades to the building’s science lab when one worker hit a gas main. All three were rushed to Jacobi Medical Center.

“Incredibly loud, a scary scene,” said Mike Allan, a neighbor living just blocks from the school. Witnesses could see materials and equipment blasted through glass windows on the upper floors at the Terrace Avenue school. The rumble was reportedly enough for residents in neighboring Spuyten Duyvil to feel it.

The explosion comes just two weeks before the start of the school year for New York City Public Schools. At a news conference several hours after the explosion, Mayor Bill de Blasio, who arrived to the blast site with officials from the School Construction Authority, Department of Buildings, and Assemblyman Jeff Dinowitz, who represents the district the school resides in, said that remains unclear.

“As we get the structural assessment, we’ll be able to let you know in the coming days,” de Blasio told reporters. “If part of the building can be opened, if all of the building can be opened, we won’t know until that full assessment is done.”

The Department of Buildings is expected to lead an assessment on structural conditions at the blast site, where its epicenter was the sixth floor.

JFK High School is home to six co-located schools that include Bronx Engineering and Technology Academy, Bronx School of Law and Finance, Bronx Theatre High School, Marble Hill High School for International Studies, New Visions Charter High School for Advanced Math and Science, and New Visions Charter High School for the Humanities. It has a student body of over 4,000.