BART trains are 15 minutes behind schedule Sunday morning while transit officials investigate a report of a fire in the Transbay Tube.

A train operator reported seeing what looked like a small fire near the Embarcadero Station at about 8:45 a.m., BART spokesman Lynton Johnson said.

BART crews have not confirmed the report but are running tests and inspections to determine what happened, Johnson said.

As of 9:30 a.m., a Pittsburg/ Bay Point train was continuing to provide limited service on a single track between San Francisco and the East Bay.