The explosion occurred at a defense factory in the city of Dzerzinsk, killing three people. Three more people are missing.
Initially, a source told Sputnik that two persons had been wounded as a result of the explosion.
"The incident occurred at a workshop specializing in the production of ammonal at the plant named after Ya.M. Sverdlov in the city of Dzerzhinsk. Two people were injured, " the source said to Sputnik.
The blast was followed by a fire that is now being extinguished by firefighters.
The Ya.M. Sverdlov plant is one of the biggest munitions factories in Russia, producing a wide range of industrial explosive materials, detonators, cumulative charges for crushing oversized materials in the mining industry as well as perforating charges for the oil and gas industry.