At least nine people have died in an explosion at a Soviet-era mine in Russia that extracts raw material for fertiliser production, the emergencies ministry said.

"The reasons [for the blast] are being investigated," Irina Gretskaya, a spokeswoman for the ministry in the Arctic city of Murmansk, said on Friday.

"After the blast a fire occurred and there were 12 people in the mine. Nine are dead and three are missing," she said.

Years of neglect after the collapse of the Soviet Union in 1991 have made made many of Russia's mines, which employ about 250,000 people, among the most dangerous in the world.

The mine where the explosion occured is operated by a company called Apatit, a major Russian producer of the phosphate mineral apatite used in making fertiliser. Apatit is part of the PhosAgro fertiliser group.

Russia's mining safety watchdog, Rostekhnadzor, said it had launched an investigation into the blast at the Rasvumchorrsky mine. An operation to retrieve bodies was under way.

Last year 110 people died in a blast in a mine in Siberia - Russia's worst mining accident in recent years.