At least three construction workers were injured in a gas line explosion at John F Kennedy High School in the Bronx borough of New York.

The injured were admitted to Jacobi Medical Center. While one person is in a critical condition, other two workers are said to be in a serious but non-life threatening state.

The explosion took place around 8 pm on Thursday when construction work was on at a sixth-floor laboratory, Reuters reported.

"This school obviously has sustained some very, very serious damage... This was part of a project being run by the school construction authority through a private contractor," CBS New York quoted Mayor Bill de Blasio as saying.

Blasio said that people in the surrounding area too felt the blast. 

"A very troubling evening for residents here in Marble Hill. They felt a blast. They felt a building shake. I talked to some of the elected officials here – they literally felt it themselves," de Blasio added.

A custodian, who was working at the site, said that he smelled natural gas just before the explosion took place. Mayor de Blasio also said that the gas led to the explosion.

"There's contractors up there. They're working up there. So they're working up there – I think they're making them do a few classrooms or something like that; chemistry room. And it just broke down when they hit it with a blow torch, and that was it," the custodian said.