The cause of the fire on Saturday at the factory near Sivakasi in southern Tamil Nadu state was not immediately known, Press Trust of India news agency reported.
The injured workers have been hospitalised.
Sivakasi is 650km southwest of Chennai, the capital of Tamil Nadu state.
Southern India has a large number of factories making fireworks, which are in great demand during religious festivals and weddings across India. They are also exported to Singapore, Malaysia, Bangladesh and other Asian countries.
Some illegal factories operate in homes because of the demand for firecrackers.