Smoke rises at the railway station in Volgograd.

The explosion occurred at 12:45 at Volgograd-1 station, RIA Novosti quoted Svetlana Smolyaninova, head of the agency of the Ministry of Internal Affairs in Volgograd.

RIA Novosti quoted local police as saying more than a dozen people were killed and many others injured, in an explosion most likely caused by a woman.

The number of people killed varies depending on the source.

Images on Russian television showed a fireball erupting in the station with a loud explosion.

`People were lying on the floor, screaming and begging for help,` a witness named Alexander Koblyakov told Rossiya-24 channel.

A witness told Interfax news agency that he saw `two bodies lying right in front of the station entrance, broken glass everywhere and there was a whole bunch of rubble there. The explosion caused a fire and firefighters rushed

Officials said metal fragments were stuffed into the bomb to increase its lethality.

Russian President Vladimir Putin ordered authorities to do everything necessary to help victims and ensure security in the city.

In October, also in Volgograd, 6 people died and 37 were injured when a woman from the Russian republic of Dagestan blew herself up on a bus.

The scene outside the station after the explosion.

While Russia was preparing to host the Winter Olympics in the Black Sea city of Sochi, terrorist Doku Umarov once called on his subordinates to carry out attacks to stop the sports festival.

Many female suicide bombers in Russia are dubbed `black widows` because they often have in common the wives or relatives of slain terrorist separatists.

Russia has for many years been fighting a wave of separatism and terrorism by extremists in the North Caucasus.

Video: The moment the station was bombed

Video: Ambulance arrives outside the station to move the victim