A bus bridge was established between the two BART stations after a report of smoke in North Concord at 12:34 p.m. prompted the closure at the end stops of the Pittsburg/Bay Point-SFO line, spokesman Jim Allison said.
Service between the two stations resumed at 1:40 p.m., Allison said.
Thick white smoke was reported from a substation about a quarter-mile from the North Concord station, but there is no confirmation that a fire broke out or what caused the smoke, Allison said.
The PG&E Sinclair Substation is located near the BART station on Port Chicago Highway in Concord.
Contra Costa County Fire Protection District firefighters responded to the smoke and BART service was shut down as a precaution, Allison said.
Firefighters have since determined the situation at the substation is safe, "so we have been able to restore train service," Allison said.