City officials say that the factory was used to produce and store high-explosive bombs for the military.
They add that the processing facility at the JSC Kristall Research Institute plant has been completely destroyed by the blast.
A factory official says five people were inside at the time, but they were safely evacuated.
Most of the people who were hurt were cut by flying glass from the explosion, which also caused a shockwave that smashed windows in homes and other factories in the city.
