Patrons on board the Millbrae bound train reported that a black male in his 50's appeared to be foaming at the mouth and might not be breathing. Officers intercepted the train and located the man, who was unresponsive. Paramedics removed the man from the train and performed CPR on the platform for about 30 minutes before pronouncing the man deceased. The SF Medical Examiner responded, but was unable to identify the man. There were no indications of foul play, and it appears that the man suffered some sort of medical emergency. The incident train was delayed for about 27 minutes.