The death toll from the Volgograd bus explosion has reached six, the press service for the Investigations Committee has reported.

"Six bodies have now been found. A criminal case has been opened based on Article 105 of the Russian Criminal Code (murder)," the press service told Interfax on Monday.

"The qualification of the case may be changed during the investigation," the source said.

The explosion occurred on a bus in the Volgograd Krasnoarmeisky district, Emergency Situations Ministry official Irina Rossius told Interfax.

The Emergency Situations Ministry's rapid reaction forces have arrived at the scene, Rossius said. The Emergency Situations Ministry rescuers have helped doctors take the wounded victims to the city's hospitals.