Trains stopped running through the station shortly before 2:30 p.m. when a person on the tracks was hit by a train, BART spokesman Jim Allison said.
The person was stuck under the train with life-threatening head injuries until San Francisco fire and medical personnel were able to free him and take him to the hospital around 3:05 p.m., Allison said.
The Richmond- Millbrae line was turned back at 24th Street station during the closure, while the Fremont-Daly City line stopped at Montgomery station in downtown San Francisco.
Trains heading toward the East Bay from south of Glen Park continued running through the station without stopping.
Allison said the station reopened and service resumed at 4:35 p.m. The collision is the second such incident on the BART tracks in 24 hours. A person on the tracks was struck at the Lake Merritt station in Oakland Friday afternoon around 2:50 p.m., stopping trains through that station for around an hour.
The victim in that incident survived the collision and was taken to the hospital, but Allison said he did not have any update on his condition.