At least 10 people have been killed in an explosion in an underground station in St Petersburg, Russian media report.
The Tass and Interfax agencies reported the blast hit at the Sennaya Ploshchad metro station, which left a number of victims.
Images posted on social media showed a train carriage with its doors blown out and damage inside.
Russian President Vladimir Putin, who is in the city, has been informed, Russian media say.
The cause of the explosion is not yet known. Russian news agencies said there may have been two blasts, with a second at the nearby Institute of Technology station.