SAN FRANCISCO -- Bay Area Rapid Transit trains between San Francisco and Oakland remain behind schedule because of a problem earlier Sunday at a power substation.

A BART spokesman says smoke was reported in the Transbay Tube after a failure at the substation on the Oakland side of the tube around 1:50 p.m. Sunday.

The problem at the substation prompted BART officials to shut down one of two lines running through the tube.

BART trains have been delayed throughout most of the afternoon and into the evening, with only trains running between Richmond and Fremont running on time.

BART officials did not know when service would be back to normal.