ST PETERSBURG, Russia (AFP) — Around 10 people were feared dead and dozens injured Monday after an explosion rocked the metro system in Russia’s second city Saint Petersburg, according to authorities, who were not ruling out a terror attack.

President Vladimir Putin said investigators were looking into all possible causes for the explosion — “accidental, criminal and first of all … terrorist.”

Pictures screened on national television showed the door of a train carriage blown out, as bloodied bodies lay strewn on a station platform.

Emergency services vehicles rushed to the scene at the Technological Institute metro station, a key transport hub.

Andrei Kibitov, a spokesman for the Saint Petersburg governor, said: “We don’t know the exact number of those killed, but it is about 10 people.”

He added that about 50 people were injured, two of which were undergoing emergency surgery.

The blast caused scenes of confusion, with traffic blocked on Moskovsky Prospect, a busy throughfare and emergency vehicles rushing to the station.

“My mom was in the metro, I don’t know what’s happened to her, I can’t get hold of her,” one woman, Natalia, told AFP outside the station as she was trying to make a phone call on her mobile.

The spokesman for Russia’s national anti-terrorism committee (NAK), Andrei Przhezdomsky, said in televised remarks that the blast occurred at 2:40pm local time (1140 GMT) and that it was looking into its causes.

Przhezdomsky said “the blast happened in a train carriage between the stations Technological Institute and Sennaya (Square),” which are next to each other on a busy line in the city centre.

The metro network announced it was shutting down entirely after evacuating all passengers and Russia’s Investigative Committee also launched a probe into the blast.

The Moscow metro also tweeted that it was “taking additional security measures” as required by law in such situations.

Putin, who was holding a meeting near Saint Petersburg in his official Strelna presidential palace, offered “condolences” to those hurt in the blast.

While there was no immediate indication as to what caused the blast, Russia’s security services have previously said they had foiled “terrorist attacks” on Moscow’s public transport system by militants, some of whom were trained by Islamic State jihadists in Syria.

And Russia’s public transportation systems have been targeted by attacks in the past.

In 2013, Russia was hit by twin suicide strikes that claimed 34 lives and raised alarm over security at the Sochi Winter Olympic Games.

A bombing at the main railway station of the southern city of Volgograd killed 18 people on while a second strike hit a trolleybus and claimed 16 lives.

A suicide raid on Moscow’s Domodedovo airport that was claimed by Islamic insurgents from the North Caucasus killed 37 people in January 2011.

That strike was claimed by the Caucasus Emirate movement of Islamist warlord Doku Umarov.

Russia beefed up its security over the holiday period in the wake of the attack on the Berlin Christmas market that killed 12.

Authorities placed heavy trucks at road intersections to block off areas where public festivities were taking place after the attack in the German capital that was claimed by the Islamic State group.

Russia has intervened militarily to bolster Syrian President Bashar al-Assad’s forces in September 2015, turning the tables on the battlefield just as rebel forces were strengthening their hold on key areas.

Russian bombardments helped the regime retake rebel areas in the east of the northern city of Aleppo after four years of fighting.

More than 310,000 people have been killed in Syria since the conflict broke out in March 2011 with protests against Assad’s rule.