A blast Monday morning at a factory in Dongtun, in Huaiyang district of central Henan province, left seven dead and 12 injured, Xinhua news agency said, quoting local authorities.
The factory was operating illegally as its licence had expired, and the family of the owner had been detained by police, it said.
Local authorities have ordered the closure of all fireworks factories in the district, the news agency added.
An explosion Sunday at a licensed fireworks factory in Yichun, in eastern Jiangxi province, also killed seven people and injured one.
The cause of the blasts was being investigated, Xinhua said.
China’s huge fireworks industry is notorious for its lax safety standards, especially among smaller producers.
Exported Chinese fireworks also do not always meet the safety standards of their destination country.
A cargo of seven tonnes of fireworks destined for Austria was judged to be dangerous and seized in November at the Dutch port of Rotterdam.