BART spokesman Jim Allison said around 11 a.m. that the Walnut Creek station was closed and trains were not running in either direction.
Someone was on the tracks for an unknown reason when a train approached the station and a collision may have occurred, according to Allison.
Officials say the person is a man in his 60s and he's on his way to the hospital. According to witnesses, this didn't appear to be malicious, but it has not been confirmed if the person jumped, was pushed or if he just fell.