The gas leak in Chhattisgarh came to light after the hospital reported it.
Seven workers fell ill after inhaling a poisonous gas at a paper mill in Chhattisgarh's Raigarh district, the police said on Thursday. The incident comes on the same day when at least 11 have died and 1,000 exposed after a gas leak overnight at a chemical plant in Andhra Pradesh's Visakhapatnam.
The incident in Chhattisgarh took place at Shakti Paper Mill in Tetla village, where the victims were cleaning an open tank on Wednesday evening, Raigarh superintendent of police Santosh Singh told news agency PTI.
However, the factory owner did not inform the administration about the incident, which only came to light after the hospital authorities alerted the police, he said.
The mill had remained was closed since the COVID-19 lockdown was enforced and the cleaning work was underway to resume operation, the official said.
The workers were admitted to a local hospital, from where three were shifted to Raipur in view of their critical condition, he said.
A team of forensic experts was dispatched to the spot to investigate the exact cause of the incident, Mr Singh said, adding that a case will be registered soon.