A blast in a St Petersburg train carriage that killed 11 people and injured 45 was carried out by a suspected suicide bomber with ties to radical Islamists, Russian authorities say.
An unidentified official told local media the suspected attacker was a 23-year-old national of an ex-Soviet Central Asian nation.
The attack on Monday (local time) coincided with a visit to the city by President Vladimir Putin. He visited the scene of the explosion late on Monday night and laid a bunch of red flowers at a makeshift shrine to the victims.
Witnesses said they saw passengers who were bloodied and burned spilling out of the train, whose door was buckled by the force of the explosion, and lying on a platform while smoke filled the station.
The bomb, packed with shrapnel, may have been hidden in a train carriage inside a briefcase, unnamed sources told local media.
The Ministry of Foreign Affairs and Trade in Wellington said they are aware of the explosion and the New Zealand Embassy in Moscow has been in contact with Russian authorities.
The confirm there is no indication at this stage that any New Zealanders have been caught up in the explosion.
White House Press Secretary Sean Spicer said the US condemned the "reprehensible" attack, while US President Donald Trump called the deadly bomb blast on a Russian subway train "absolutely a terrible thing".
Russia's National Anti-Terrorist Committee said an explosive device was found at a different metro station, hidden under a fire extinguisher, but had been made safe.
Russia has in the past experienced bomb attacks carried out by Islamist rebels from Russia's North Caucasus region. The rebellion there has been largely crushed, but Russia's military intervention in Syria has now made it a potential target for Islamic State attacks, security experts say.
The blast raised security fears beyond Russian frontiers. France, which has itself suffered a series of attacks, announced additional security measures in Paris.
Soon after the blast happened at 2:40pm on Monday, ambulances and fire engines descended on the concrete-and-glass Sennaya Ploshchad station. One helicopter hovered overhead and then landed on a broad avenue to take away an injured passenger.
"I saw a lot of smoke, a crowd making its way to the escalators, people with blood and other people's insides on their clothes, bloody faces," St Petersburg resident Leonid Chaika, who said he was at the station where the blast happened, told Reuters by phone. "Many were crying."
A huge hole was blown open in the side of a carriage with metal wreckage strewn across the platform. Passengers were seen hammering at the windows of one closed carriage.
If it is confirmed that the bomb was carried out by radical Islamists, the Kremlin is likely to argue the attack underlines the importance of its campaign in Syria, where it is backing President Bashar al-Assad in a fight against Islamist militants.
But some sections of Russian society may see the metro bombing as proof that Putin's decision to intervene in Syria has again made Russian civilians into targets.
Two years ago, the Islamic State group said it brought down a plane carrying Russian tourists home from a Red Sea resort. All 224 people on board the flight were killed.
An attack on St Petersburg, Russia's old imperial capital would have some symbolic force for any militant group, especially Islamic State or Chechen secessionist rebels.
Reuters / Newshub.