A nail bomb thrown onto a train by a suspected terrorist has ripped through a carriage in St Petersburg killing at least 12 people and injuring 50 more today.

The terrifying incident, which is being investigated as a terror attack, took place on a train that was travelling between Sennaya Ploshchad and Sadovaya metro stations.

The attack has left dozens injured, including children, and witnesses described seeing a man throwing a backpack onto the train moments before the explosion and a second explosive device was found and made safe in a nearby station.

Russian security agencies did find an explosive device at a different metro station in central St Petersburg and made it safe, the National Anti-Terrorist Committee said in a statement.Eight bodies were recovered from the carriage while two more were found on the platform and the final two killed were found in the tunnel