The blast took place on Tuesday afternoon in the Hunan province city of Hengyang and its cause was under investigation, the official Xinhua News Agency said.
A Hengyang city policewoman surnamed Xiao confirmed the accident on Wednesday and said no civilians were injured. The armory is in a rural township on the outskirts of Hengyang.
China's military operates with a high degree of secrecy and information about explosions, plane crashes and other accidents is usually tightly controlled.
With 2.3 million members, China's military is the world's largest. It has enjoyed massive upgrades to equipment and living conditions for soldiers, fueled by two decades of soaring defense spending. Despite that, conditions for much of the sprawling land-based forces remain basic and oversight is often lax.
While the explosion was called an accident, Chinese security forces have come under attack in recent years from Islamic extremists fighting for independence for the northwestern region of Xinjiang.