Ten people have been reportedly killed and several others injured after a bomb blast hits a metro station in Russia's St. Petersburg.

According to preliminary information released by Russia’s TASS news agency, rescue teams were being dispatched to the site of the blast, with a witness telling Reuters that eight ambulances were seen near the Sennaya Ploshchad metro station.

Another Russian news agency, RIA Novosti, however, reported that there had been apparently two separate explosions at two metro stations.

Three metro stations have been closed, according to Fontanka local media outlet.

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

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.

“I have already spoken to the head of our special services, they are working to ascertain the cause (of the blasts),” Putin said at a meeting with Lukashenko, adding, “The causes are not clear, it's too early. We will look at all possible causes, terrorism as well as common crime.”

An injured person is helped by emergency services outside Sennaya Ploshchad metro station, following explosions in two train carriages at metro stations in St. Petersburg, Russia, April 3, 2017. (Photo by Reuters)

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.

Later on, an unnamed source in Russia's emergency services was quoted by Reuters as saying that there was only one blast in St. Petersburg's metro system, which happened on a train between two stations.

"There was one blast in one site in between (stations) as the train arrived at the Technology Institute station from Sennaya (Ploshchad) station," the source added.

Meanwhile, Russian security agencies reported that they had found an explosive device at a metro station in central St. Petersburg and made it safe.

A statement by the National Anti-Terrorist Committee said in on Monday that the device was found at the Ploshchad Vosstaniya metro station, which was a different location from where a blast earlier took place.

Russia’s public transportation system has been targeted by attacks in the past.

In December 2013, twin separate bombings a day apart claimed the lives of 34 people in Russia’s southern city of Volgograd.

The first bombing at the main railway station of Volgograd killed 18 people while the second strike hit a trolley bus and claimed 16 lives.

The attacks followed a bus bombing carried out in the same city two months earlier.

In January 2011, an attack on Moscow’s Domodedovo airport, claimed by militants from North Caucasus, killed 37 people.

(source: presstv)