Seven people were killed and four were critically injured after an explosion at a firecracker factory in Tamil Nadu’s Cuddalore district, NDTV reported. The police said the factory owner also died in the incident.

The factory is in Kattumannarkoil town of the district, 190 km from state capital Chennai. “It is a licenced unit near Kattumannarkoil,” Cuddalore Superintendent of Police Sree Abhinav said. “All of them were workers. Investigation is on into whether they were making country-made bombs and whether they were using only permitted explosives.”

An investigation is underway to establish the reason the explosion occurred.

More details are awaited.