BOSTON -- One person was shot Friday after gunfire broke out on a Massachusetts Bay Transportation Authority bus in Dorchester on Friday afternoon, officials said.

Boston Police Commissioner Ed Davis said an 18-year-old male was shot on the bus near Washington Street and Dorchester Avenue at about 3:50 p.m.

Officials said that they believe the gunman was outside of the bus at the time.

"There were reports of a group of black males running from the scene, and we are currently investigating the places where they may have gone to," Davis said.

The victim was transported to Boston Medical Center, where he was being treated for life-threatening injuries.

The shooting happened on the same afternoon that the Guardian Angels, an anti-crime group based in New York, started bringing their message of peace to the streets of Boston.

Officials said they were searching for several people in connection with the shooting.

NewsCenter 5 and TheBostonChannel.com will have more information as it becomes available.