Gas Explosion at New York City High School Injures Three

8/21/2015_BronxGasExplosion
FDNY work outside after an explosion at John F. Kennedy High School in the Bronx borough of New York August 20, 2015. The gas line explosion at the high school on Thursday injured three construction workers, one critically, authorities said. Shannon Stapleton/Reuters

(Reuters) - A gas line explosion at a New York high school on Thursday injured three construction workers, one critically, and badly damaged at least three floors of the building, authorities said.

The explosion occurred at about 8 p.m. EDT at John F. Kennedy High School in New York's Bronx borough while construction work was going on in a sixth-floor laboratory, a police spokesman said.

A fire department spokesman said all three of the injured were taken to Jacobi Medical Center, two with non-life-threatening injuries.

New York City Mayor Bill de Blasio, who held a press briefing from near the school, said the Department of Buildings would evaluate the structural integrity of the building.

"This school obviously has sustained some very, very serious damage," he said.

At least three floors were damaged, police said.

The New York school year starts on Sept. 9., and it was too soon to know if the building would be safe enough for students come first day, officials said.

The school serves more than 1,200 students in grades 9-12, WABC-TV reported.