Fifteen people were hospitalised but none had life-threatening injuries, it said. A first explosion soon triggered two other blasts at the same facility at 11:45am Moscow time on Saturday, before spreading to another building nearby.
At a different armament factory in Dzerzhinsk, five people died in August past year in an explosion.
The deputy governor of the Nizhny Novgorod region, Dmitry Krasnov, told Russian state television that "two people are missing".
Earlier health ministry officials told news agencies that the wounded had "shrapnel wounds of mild and moderate severity" and that they were receiving medical assistance.
Russia's Investigative Committee said that those were man-made explosions.
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The blast broke windows in about 200 homes near the plant, the Interfax news agency cited regional authorities as saying.
Representatives of Kristall told Interfax that five people were working in the area where the explosion occurred and were safely evacuated.
Eighty-five people have been injured with 15 treated for shrapnel wounds after a factory blast in central Russian Federation.
More than 300 people and 50 technical units responded to the blaze, which covered over 8,500 square feet and took firefighters several hours to contain, according to local media.
The Ministry of Emergency Situations said the fire is now spread over a 100 square meter area.
Smoke rising from the site of blasts at an explosives plant in the town of Dzerzhinsk.