Ten people have been killed following blasts on the underground rail system in St Petersburg.
Interfax and RIA news agencies said two explosions have been reported on the Russian city's Metro.
Reuters said blasts took place in two train carriages at two stations.
All the stations on the St Petersburg Metro have now been closed, it has been reported.
The Governor's press office confirmed that 10 have died and said a further 50 have been injured.
Video showed injured people lying bleeding on a platform, while other footage showed people fleeing from platforms amid clouds of smoke.
Russian president Vladimir Putin, who is in the city to meet the Belarussian leader, confirmed there are dead and injured.
He expressed his condolences and said he had spoken to the heads of the security services, who are trying to establish the cause.
He said: "I have already spoken to the head of our special services, they are working to ascertain the cause (of the blasts).
"The causes are not clear, it's too early. We will look at all possible causes, terrorism as well as common crime."
At least one of the devices was filled with shrapnel, according to an Interfax source.
A Reuters witness said they saw eight ambulances near the Sennaya Ploshchad station and footage broadcast on local TV showed activity by the authorities outside the station entrance.
The St Petersburg underground railway said in a statement: "An evacuation from the stations is ongoing, there are people injured.
"An unidentified object supposedly blew up in a (train) carriage."
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