Local media agencies reported a blast at the Sennaya Ploshchad metro station, which left a number of victims.
At least 10 people were injured, the RIA news agency reports, while Interfax reported there appear to have been blasts at two metro stations.
Images posted on social media showed a train carriage with its doors blown out and damage inside.
A live stream on the Russian website Life News said there had been either one or two explosions around 2.30pm local time.pet
More to follow..