Two staffers and five Nyack College students were hurt in the blast Tuesday, WCBS-TV, New York, reported. Their injuries included fractures, burns and damage from pieces of metal.
The explosion occurred in the Sky Island lodge on the campus in South Nyack, a town on the Hudson River a few miles north of New York City.
"We're just so thankful that school was out because if this was a month ago, it would've been fully staffed," South Nyack Mayor Bonnie Christian said.
Mike Donovan, a spokesman for Orange & Rockland Utilities, said the explosion appears to have occurred in an underground gas main and traveled through sewer or storm drains to Sky Island Lodge. He said workers late Tuesday found a damaged gas line that serves the school gymnasium.
"We found that the connection for the service line had pulled out of the main, had pulled out of it's fitting in the underground construction and had released a significant amount of gas," he said.