The victims were workers of the unit at Narayanapuram village, four kms away from Sivakasi, the country's fireworks hub, and they were engaged in making crackers when the explosion occurred.
The explosion apparently occurred due to friction among the chemicals, police said, adding, the unit was completely damaged under its impact.
The injured were in a critical condition and they have been admitted to government hospital. It was investigated whether the unit had licence to make crackers, police said.