An MBTA spokesperson said the train operator stopped the train after they spotted a downed wire in the tunnel.

Hundreds of passengers aboard the Blue Line were evacuated Tuesday afternoon after a train became stuck beneath the Boston Harbor, between the Maverick and Aquarium stations, officials said. Over the course of about an hour, Boston firefighters assisted with the evacuation of 500 people from the disabled train, the department said.

The head of the MBTA said more problems were uncovered during an investigation into a Blue Line train evacuation​ that happened on Tuesday.