A Massachusetts Bay Transit Authority Green Line train derailed at the Lechmere station in Cambridge on Tuesday, injuring seven people on board.

The derailment occurred at 5 p.m., the MBTA posted on X.

The wheels of the train’s lead car went off the tracks, the MBTA told Boston NBC affiliate WBTS. About 50 people self-evacuated and walked to an emergency exit along the tracks.

The Cambridge Fire Department responded to the scene, shutting off the power to the train, medically evaluating the evacuees and transporting the injured to hospitals. Fire officials said in a post on X that the injuries weren’t life-threatening.

Transit officials believe human error, not the track itself, was the cause of the derailment.

“So right now, all of the track structure, all the measurements indicate that track was not a factor in this incident. I look at the operator, the train operator, for how they were operating the train. … Operators are expected to follow operating rules, speed limit compliance,” MBTA Chief Operating Officer Ryan Coholan said at a press conference.

In a statement to Boston CBS affiliate WBZ-TV, the MBTA said it “sincerely apologizes to riders for the frustration and distress this incident has caused. We are committed to thoroughly investigating this matter to ensure this does not happen again.”

The National Transportation Safety Board said on X that one of its investigative teams would arrive by Wednesday to determine the exact cause of the derailment.

• Brad Matthews can be reached at bmatthews@washingtontimes.com.