San Francisco police began chased an armed robbery suspect who had stolen a laptop onto the platform and then the tracks between the 16th Street Mission and 24th Street Mission stations shortly before 5 p.m., BART spokeswoman Alicia Trost said.
The search prompted the shutdown of all BART service between the Powell and Daly City stations, Trost said.
Trains heading into San Francisco were turning around at the Montgomery station and heading back toward the East Bay, Trost said.
Trost said that as of about 5:30 p.m. BART service had resumed through all San Francisco stations after police concluded the search without finding the suspect.
The up to 50-minute delays have caused crowding on the platform and BART stations are holding passengers at some stations from entering the paid area or going down to the platform, Trost said.