The 50- to 60-year-old steel cable probably “weakened until the point where it came down” after decades in a damp, subterranean tunnel, said Phillip Eng, the MBTA general manager.

More than 450 MBTA passengers were evacuated from a Blue Line train in the tunnel under the Boston Harbor due to a signal issue Tuesday afternoon.

Around 500 MBTA riders were reportedly stuck on a Blue Line train Tuesday afternoon, according to officials. The train was disabled under the Boston Harbor between Maverick and Aquarium stations, the Boston Fire Department reported. It took firefighters about an hour to evacuate the 500 people through the tunnel.