Fire and rescue authorities say the factory could have violated fire safety norms.
Four people, including two women, died in an explosion at a licenced cracker factory at Chinappampatty in Tamil Nadu's Salem district on Tuesday evening.
Two other women suffered severe burn injuries.
The fire has been brought under control.
"We are investigating. The unit has licence till 2018. One of the women who died is the wife of the factory owner," said Amit Kumar District Superintendent of Police.
The factory is in the midst of an agricultural farm without electricity connection. Fire and rescue authorities say the factory could have violated fire safety norms.
District Fire Officer T Venkataraman said, "The accident happened around 8 PM. Clearly it appears the factory was functioning at that time. It is a violation as they can't work beyond 6 PM."