Soon after the accident, Wang Jinshan, secretary of the provincial committee of the Communist Party of China, and provincial governor Wang Sanyun rushed to the scene to organize rescue operation and investigation.
All the injured were sent to the hospital.
One of the three seriously wounded suffered a spleen burst and the other two had serious fractures, but they are in stable conditions, doctors said.
The privately-owned company had about 60 employees and started production in 2003, registering 20 million yuan in fixed assets.
It processes about 30,000 tonnes of quartz sand annually, which are sold both in domestic market and in southeast Asia and Europe.
The company has halted operation and its yard is cordoned off.
Police were questioning Cao over the source of the explosives and investigating how they went off.
