The Tongxu county government in Henan province said the cause of Thursday's blast was not immediately clear and under investigation, the Associated Press reported.
China is less than a month away from New Year celebrations, when holiday revelers set off fireworks. There are frequent fireworks-related incidents at factories in the weeks leading to the holiday, as China generally has a poor record in workplace safety.
On Wednesday, an explosion at a machinery factory killed four workers in the eastern city of Shanghai.
Tongxu County was in the spotlight recently when local authorities ordered the demolition of a gigantic statute of communist revolutionary Mao Zedong, after the structure drew sneers from a large segment of the public.