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A BART train unexpectedly shut down in between stations in San Francisco on Monday afternoon, creating massive delays in the transit system and forcing passengers on board to wait 30 minutes for the train to be pushed to the next station so they could get off.

The Fremont-bound train was in a tunnel between Glen Park and the 24th Street Station in the Mission District when it broke down about 3:10 p.m., said BART spokesman Taylor Huckaby. It was not immediately clear what caused the mechanical failure or how many people were on board at the time.