Two workers were killed in a gas leak at a factory on Wednesday in Khardah, around 16km north of Kolkata, police said.
The incident took place around 12pm during maintenance work at the Electrosteel Castings Ltd (ECL) factory on BT Road in North 24-Parganas district, they said.
The deceased were identified as Ranjit Singh (30) and Swapnadip Mukherjee (41), police said.
It is suspected that a carbon monoxide gas leak led to the deaths of two people while one other was taken ill, Barrackpore's police commissioner Ajoy Thakur said after visiting the area.
The injured person, identified as Rohit Mahato, is critical and undergoing treatment at a hospital.
Police said they are investigating the matter.
The company, which manufactures ductile iron pipes at the facility, is yet to comment on the incident.
The incident led to tension in the area with locals raising concerns about the safety measures at the nearby factories.