At least 14 people were killed and dozens more were injured after an explosion ripped through a St Petersburg metro station on Monday.

Video footage on social media showed terrified passengers attempting to help the wounded. A huge hole was created in the side of one carriage with mangled metal wreckage strewn around the platform.

"People were bleeding, their hair burned," one eyewitness told LifeNews.

"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."

Where did the explosion occur?

The St Petersburg metro press office said the blast was caused by a shrapnel-loaded explosive device, adding that all stations had been shut down after the incident. The city's airport was also closed.

According to local media reports, the explosion occurred near Sadovaya and Sennaya Ploshchad stations.

Initial reports said there were two explosions, but a Russian emergency services source later disputed this in an interview with local media.

The home-made explosive device was thought to be equivalent to 200 grams of TNT and was placed on the carriage.

Bomb disposal squads defused a second device found by metro staff at another station.