The incident happened around 7.30 am at an illegal leather unit at Malancha-Padmapukur in the Bhangore police station area, around 20 km from Kolkata.
Three of the injured were in very critical and being moved to Kolkata for treatment. The others are being treated at a hospital in the district.
After the incident had taken place, the factory has been sealed. It is suspected that gas cylinders kept inside the factory were went off. A forensic examination had need to underway to know the exact cause of the blast.
Also, a huge team of police has been positioned in the area and further investigations are underway.