At least ten people were killed and several others injured in an explosion inside a metro train at the Sennaya Square station in Russia's St. Petersburg.
TASS news agency reported that an unidentified device exploded in a train car.
Evacuation is under way at a blast-hit subway station. Rescue workers and law enforcement personnel are working at the scene.
Seven metro stations in the city have been closed following the blast.
Meanwhile, President Vladimir Putin has been informed about explosion.