At least six workers died after a poisonous gas leaked at a privately-owned steel mill in Anantapuram district of Andhra Pradesh on Thursday. District Superintendent of Police G Ashok Kumar told PTI that the incident took place while testing was being conducted following maintenance operations.

“As per preliminary information, two workers died on the spot and four others in hospital,” Kumar said. “Carbon monoxide is the main gas used for reheating process and its leak caused the mishap.” There is no information about how many workers were injured, but rescue operations are being carried out, he added.

The steel mill, located in Tadipatri town, belongs to Brazilian firm Gerdau, a producer of long steel. Andhra Pradesh Deputy Chief Minister (Home) N China Rajappa condoled the deaths.