According to KRON 4 News, a BART train partially derailed between the Lake Merritt and 12th Street BART stations. Passengers are being evacuated out of the tunnel. The derailed train was headed for Richmond.
No word yet on any injuries or cause of derailment. SFist will update with more as soon as information becomes available.
Update: CBS 5 reports: "Officials say there have been no initial reports of serious injury." BART spokesman Liniton Johnson describes the derailment as "very minor," saying that BART trains "go very slowly through that area" and that it has caused "minor delays."