A natural gas explosion sent flames shooting through a Northeastern University (search) dormitory Wednesday, injuring seven people and severely damaging the six-story brick building.

Victims were treated for broken bones, cuts and burns, but no one was seriously hurt, said Richard Serino, Boston's emergency services director.

A Boston Fire Department (search) spokesman said the explosion probably was caused by a gas leak in the boiler room of Kerr Hall.

Alex Zinni, a 23-year-old from Mansfield (search), said he was eating lunch when black smoke and orange flames filled the second-story dining hall.

"I was tossed up, tossed down, and I heard people say, 'Go!"' said Zinni, who was unhurt. "I felt like I was lifted."

Kerr Hall houses dormitories and a faculty center. The injured included students, faculty, staff and a utility worker sent to investigate the gas leak.

Part of the first floor collapsed, Deputy Chief Kevin MacCurtain said, and the building was evacuated because of suspected structural damage. Damage was estimated at $800,000.

KeySpan Corp. was doing work on the gas line Wednesday before the explosion, university spokeswoman Laura Shea said. A spokesman for the utility company did not immediately return a call seeking comment.