At least seven workers were killed on Tuesday while cleaning a tank in a private dyeing unit in Tamil Nadu's Erode district, police said.
Police said the incident was occurred at KPR Mill's dyeing unit, where workers were called to repair a faulty pump in the tank.
One worker who went inside to check the motor fainted immediately, while others who went in to check upon him also lost their lives, they added.
The dyeing unit is located at Erode's industrial estate of SIPCOT (State Industries Promotion Corporation of Tamil Nadu) near Perundurai. Erode is at least 400 km from state capital Chennai.
Police suspect the worker died after inhaling some poisonous gas.
They said seven bodies have been shifted to a government hospital for post-mortem examination.
Seven other workers have also been admitted to the hospital and their condition is reported to be serious, a police official in Erode said.
No official of the factory was available for comment.