The Tongxu county government in Henan province said Thursday that a team was set up to investigate the blast. Its cause was not immediately clear.
China is less than a month away from new year celebrations, when holiday revelers set off fireworks to ring in the new lunar year. Often, there are reports of fireworks-related incidents at factories in the weeks leading to the holiday, as China generally has a poor record in workplace safety.
On Wednesday, a machinery factory was hit by an explosion that killed four workers in the eastern city of Shanghai.
