Most of the victims were female workers who were assembling fuses for firecrackers, the official Xinhua News Agency said.
It said the blast took place on Friday and reduced the factory in the city of Cenxi in the Guangxi autonomous region into rubble.
A man reached at the Guangxi Work Safety Bureau said that two executives of the factory have been detained.
He only gave his last name as Chen, which is common among China's bureaucrats when speaking to the press.
Workplace safety is a major problem in China where enforcement of laws is lax with factories themselves usually left to decide whether to follow them.