Police received reports of a gunshot victim in the parking lot there at 6:50 p.m., Deputy Police Chief Ben Fairow said.
Trains were held at the station and other trains were not permitted to enter the station while police investigated and ensured that a possible suspect was not departing on a train. Trains have now resumed normal service.
The victim was taken to John Muir Medical Center in Walnut Creek with life-threatening injuries, Fairow said.
A section of the parking lot remains cordoned off tonight while officers gather evidence and interview witnesses.
Pittsburg police and the Contra Costa County Sheriff's Office are assisting BART police in the investigation.
