DEVELOPING: Several people were injured Tuesday in a slow-speed commuter train collision at Boston's South Station.

The accident happened about 9:15 a.m. when a Massachusetts Bay Transportation Authority train struck a barrier as it was coming into the station.

The train was entering at a "very slow rate of speed" when it hit the rubber bumper, MBTA spokesman Joe Pesaturo said. He said some people were waiting to exit the rail car and fell after the collision.

Between 15 to 20 people were being treated Tuesday morning for minor injuries, according to fire department spokesman Steve MacDonald.

Pesaturo said it was too soon to know the cause of the crash. He said the engineer will be tested for alcohol and drugs, which is standard procedure.

The station has not been closed.

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The Associated Press contributed to this report.