Transit police are investigating after an MBTA Red Line train loaded with passengers left Braintree station Thursday morning and traveled through four stops north without an operator.

Investigators are looking into an initial report that someone may have tampered with a safety device in the train cab, according to a statement from the MBTA.

No passengers were reported injured, according to the MBTA.

Officials are interviewing "several people," including the train's operator, Gov. Charlie Baker said on Boston Herald Radio. Baker said multiple times that the train had been tampered with but said he couldn't go into details because the investigation was ongoing.

"This train was tampered with, and it was tampered with by someone who knows what he was doing," Baker said.

"This was an isolated incident, a tampered train, tampered by someone, and we'll get to the bottom of it, and I'm sure we'll have more to say about it shortly," the governor said. "Hopefully by the end of the day."

The inbound train left Braintree at approximately 6:08 a.m., according to the MBTA, making no station stops and traveling to just past North Quincy station.

MBTA operations staff then shut off power to the third rail, bringing the train to a complete stop, according to the transportation agency.

T personnel boarded the train and operated it to the next stop, JFK/UMass, where passengers were asked to exit.

"Passenger safety is the highest priority for the MBTA and this highly troubling incident is under investigation by Transit Police detectives," MBTA General Manager Frank DePaola said in a statement.

Baker said his administration is working with law enforcement on the investigation.

"I think all the right people are currently being investigated," he said.