Russian President Vladimir Putin said all possible causes, including terrorism, are being considered in the investigation into two blasts that killed at least 10 people and left dozens injured, according to Russian media.

An injured person stands outside Sennaya Ploshchad metro station, following explosions in two train carriages at metro stations in St. Petersburg, Russia April 3, 2017.??[Photo/Agencies]

Putin, who was in St Petersburg around the time of the blasts, which hit the subway stations of Sennaya Ploshchad and the Institute of Technology, said he had conferred with advisers.

"Security forces are working and doing what they can to ascertain what happened and make a complete assessment of the situation," he was quoted by the BBC as saying.

Pictures posted on the internet showed a train with twisted and buckled doors, and people lying on the station platform, apparently seriously injured.

All of St Petersburg’smetro stations were closed and passengers evacuated, the BBC said.

In Moscow, subway authorities were taking extra security precautions and had offered assistance to their colleagues in St Petersburg.

The St Petersburg metro consists of five lines and carries about two million passengers a day.