A bomb blast which occurred at St. Petersburg metro station in Russia has left no fewer than ten people dead and several others injured.

The St. Petersburg metro in a statement carried by Russian news agencies, said "An unidentified object supposedly blew up in a (train) carriage. An evacuation from the stations is on-going, there are people injured.”

Another report by St. Petersburg emergency services indicated that there had been blasts in two train carriages at two metro stations.

Russia’s Interfax news agency cited a source as saying that at least one of the blasts involved a device filled with shrapnel, adding that at least 50 people had been injured.

Russian President Vladimir Putin has issued a message of condolence, sympathizing with the families of those killed in St. Petersburg subway explosion.

Putin is currently in St. Petersburg for a meeting with his Belarusian counterpart, Alexander Lukashenko.

Speaking to reporters, he said the cause of the blasts was not clear yet, adding that all possibilities, including terrorism, were being considered.

Putin at a meeting with Lukashenko said “I have already spoken to the head of our special services, they are working to ascertain the cause (of the blasts).

He added, “The causes are not clear, it';s too early. We will look at all possible causes, terrorism as well as common crime.”

 * Emergency vehicles and a helicopter are seen at the entrance to Technological Institute metro station in Saint Petersburg on April 3, 2017. (Photo by AFP)

Early videos showed injured people lying bleeding on a platform to be treated by emergency services while others ran away from the platform amid clouds of smoke.

The metro network servicing Russia';s second largest city said in a statement later on Monday that it had closed all stations at 15:40 local time (12:40 GMT) to facilitate an ongoing evacuation operation. It is still unclear when the underground system will open again.

Following the incident, Moscow';s deputy mayor told media that authorities in the Russian capital were taking steps to tighten security on Moscow subway.

No group or individual has assumed responsibility for St. Petersburg metro blasts yet.