BART personnel received a report at about 7:30 a.m. of an unattended dog on a train headed to San Francisco.
When the train stopped at the Lake Merritt station, the dog got off the train and jumped onto the tracks before authorities could capture it, BART spokesman Jim Allison said.
The dog ran through a tunnel toward the West Oakland station, and all BART trains headed to that station stopped while authorities searched for the animal, Allison said.
The dog was not found, but BART officials believe it may have gotten off the tracks at the West Oakland station, he said.
Trains were delayed by up to 10 minutes during the search. Regular service resumed after authorities confirmed the dog was not on the tracks, and trains were back on schedule by about 8:30 a.m., Allison said.
BART officials want to remind customers that dogs other than service animals are not allowed on trains unless they are in carriers approved for transport.