BOSTON -- A power outage forced MBTA officials to close down parts of the Green Line on Saturday afternoon, cutting off subway service through Boston’s back bay and stranding dozens of passengers underground.

MBTA officials said the electrical problem was caused by an overhead power cable near Arlington Station at about 4 p.m. Service was shut down between Kenmore Station and Park Street during the outage, and MBTA buses took passengers along the route until service was restored two hours later.

Matthew Campion said he was traveling underground when the power outage stranded his Green Line trolley between Copley Station and Arlington Station. Campion and the other passengers waited for about an hour before they were taken off the trolley and escorted back through the tunnel on foot to Copley Station, he said.

MBTA spokesman Joe Pesaturo confirmed that passengers from at least one trolley were evacuated through the tunnels when service was shut down. Pesaturo said service was delayed 25-30 min on the rest of the Green Line by the power outage.

The Green Line began running again at 6:15 p.m. after repairs were made.