[Update: BART has resumed normal service.] Yikes! Two of the five Bart lines have been shut down this afternoon due to a medical emergency on a train at the Embarcadero station. "The Richmond to Daly City and Fremont to Daly City lines are stopped while crews attend to an unconscious person on the floor of a train car stopped at Embarcadero station," notes The Chronicle. "The medical emergency occurred around 2 p.m. and BART police responded to the scene."

If you're travelling between San Francisco and the Easy Bay, BART suggests the following: "take the Pittsburg / Bay Point - SFO line or the Dublin / Pleasanton."

We'll update as soon as we know more. Brace yourselves for a (possibly) hellish commute.

Update: The medical emergency was that a man has died. The Chron goes on to explain: "Around 2 p.m., a man riding a train toward Millbrae was found slumped forward in his seat." When paramedics arrived he was pronounced dead at the scene.

UPDTE II: BART has resumed normal service. Expect residual delays.