Boston fire crews responded to the scene just before 10:30 a.m. They said the outbound car was in the tunnel when the derailment occurred.
Fire officials said there were no injuries reported. One person required assistance evacuating.
MBTA crews were working to put the trolley back on the track. Delays were expected as shuttle buses replaced the B-Line between Blandford Street and Copley stations. All Green Line service was also replaced with shuttle buses between Kenmore and Copley in both directions.
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