A gas line explosion at a New York high school on Thursday injured three construction workers, one critically, 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.

The police spokesman said there was damage to two non-load-bearing walls. The New York school year starts on Sept. 9.