Boston transit officials say a train without an operator but with passengers on board left a suburban station and traveled through several other stations without stopping before it was disabled.

The MBTA said no one was injured.

The Red Line train left the Braintree Station south of Boston just after 6 a.m. Thursday and was eventually stopped just past North Quincy Station when T personnel shut off power to the third rail.

T personnel boarded the train, and drove it north to the JFK/UMass stop, where passengers disembarked. The train was taken out of service for an investigation.

Massachusetts Bay Transportation Authority General Manager Frank DePaola called it a "highly troubling incident."

The initial investigation indicates that a safety device within the train's cab may have been tampered with.