Police are hunting two suspected terrorists accused of planting explosive devices in St Petersburg metro stations - one of which detonated in a train killing at least 11 and injuring 50 last night.
Several Russian media outlets have released the CCTV picture of the bearded suspect who was wearing a long, black gown-like top and a hat. He is blamed for caused the carnage by detonating a bomb packed with shrapnel.
The terrifying explosion happened on a train travelling between Sennaya Ploshchad and Sadovaya metro stations. A second explosive device disguised as a fire extinguisher was found and defused in a nearby station, Daily Mail reports.
Nobody has claimed responsibility for the explosion, but previous attacks on Russia have been blamed on Isis and Chechens.
A search warrant has been issued for two people in connection with the attack - one for planting the bomb that detonated at Sennaya Ploshchad and the other for leaving an explosive device at Ploshchad Revolyutsii station.
A source said: "Two people are being sought on suspicion of planning the blasts, one of whom is thought to have placed the explosive device in the metro wagon and the second person for leaving a bomb at the metro station Ploshchad Revolyutsii."
Dozens have been injured, including at least three children. It was reported the man left a briefcase on a train before moving carriages moments before the deadly blast.
Bloodied passengers were strewn across the platform in the Russian city as emergency services scrambled to save those wounded by the bomb and the resulting shards of glass and twisted metal.
Vladimir Putin is in his hometown of St Petersburg today for talks with the president of Belarus and confirmed "there are dead and injured", offering his condolences to the families of those killed.
The Kremlin leader, who wanted to visit the scene after the attack but was held back by security services, 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."
Interfax news agency cited an unidentified source who says the suspect in Monday's blast might have left the explosive device in a bag.
Russian online news outlet Fontanka published a grainy photo that shows a middle-aged man who entered Petrogradskaya station 20 minutes before the blast.
Interfax news agency earlier quoted a source as saying that surveillance cameras had captured photos of the blast suspect.
At this stage it is not clear whether or not the suspect was wearing the hat and gown as a disguise.
Kremlin spokesman Dmitry Peskov denied earlier speculation that Putin was due to pass by the Sennaya Metro station around the time of the blast.
The explosion happened between the Sennaya Ploshchad station and Tekhnologichesky Institut about 2.40pm local time, Russia's National Anti-Terrorism Committee said.
A witness told Russia's Life News: "People were bleeding, their hair burned. We were told to move to the exit, because the movement stopped. People just fled.
"My girlfriend was in the next car that exploded. She said that he began to shake. When she came out, she saw that people were mutilated."
Another witness said: "It's just like a war here. Every special service is here, the FSB, police, and multiple - really a lot of them - ambulances.
"I don't think I've ever seen to many paramedics in my life. Something completely horrible is happening here."
Eight bodies were recovered from the carriage and two more were found on the platform or were in the tunnel.
Earlier reports indicated a backpack had been thrown onto the train and witnesses also suggested there had been multiple explosions, but officials confirmed just the one blast.
Russian security agencies did find an explosive device at the Ploshchad Vosstaniya metro station in central St Petersburg and made it safe, the National Anti-Terrorist Committee said.
Other witnesses also described a man leaving a briefcase on one carriage before moving to another just seconds before the huge explosion.
As reports of the suspected terror attack trickled through to the capital, Moscow heightened its security and local reports suggested three metro stations - Nagatinskaya, Savelovskaya and Ugrezhskaya (CIP) - were cordoned off because of suspicious packages.
The Life website showed pictures of blown-out train doors and several injured people on the station platform.
Polina, who was in the carriage next to the where explosion erupted, said: 'There was quite a lot of people in the carriage: everyone was sitting, some were standing.
"The explosion occurred between Sennaya and Technological Institute stations.
"There was a deafening boom, and then a strong odour and smoke.
"We immediately went to another end of the car. It was very crowded.
"Everything was happening on the move, the train didn't stop. At Technological Institute everyone got off.
"We saw that the next car was teared apart, windows were broken, no lights, blood. People were dragged out of it, some were carried, some were walking with support.
"There was a lot of injured. I don't know if there were dead, we left in about two minutes."
There were fears a second, unexploded bomb was left on a platform on the network in St Petersburg, but it was an abandoned bag.
A subway worker who asked not to be named told local press: "The second carriage exploded.
"The explosion was such a force that the flesh burned, people were in scrapes of the flesh, blood everywhere."
Another witness said: "Many people have sandy traces on their faces.
"Its not clear what bomb it was, no one figured it yet. People are panicking, many are calling their mothers."
Anna, who was at the station at the moment of explosion: "People were lying down, all black, scary, with a horrible smell of burned flesh."
Another eyewitness said: "Everyone was ready for death in the metro carriage.
"After the explosion everyone was waiting for the consequences. Then we were taken out, people started helping each other, walking others out, most of them were in blood."
The leader of the Kremlin is visiting the city today and is expected to hold talks with the Belarusian president later in the day.
Sennaya Ploshad is one of the Russian city's main metro stations, where three underground lines connect.
It is beneath the large Sennaya shopping centre as well as the offices of Gazprombank, Russia's third-largest bank.
The St Petersburg metro said it had closed the neighbouring Technological Institute and Sennaya Ploshchad stations.
Following the reports, the Moscow metro also announced that it is "taking additional security measures" as required by law in such situations, according to the network's official Twitter account.