NEW DELHI, July 13 (Xinhua) -- At least six workers were killed and few others fell unconsciousness Thursday after inhaling poisonous gas that leaked inside a factory in southern Indian state of Andhra Pradesh, police said.

The leak took place inside a private steel plant rolling unit at Tadipatri in Anantapur district, about 384 km west of Amaravathi, the main city of Andhra Pradesh.

"This evening due to poisonous gas leak inside factory six workers were killed and few others taken ill," a senior police official posted in Anantapur said. "The mishap occurred while testing was being done after maintenance work at the unit."

Officials say the workers inhaled carbon monoxide, which got leaked due to mishandling.

"Few workers fell unconscious and have been hospitalised," the official said.

The steel mill belongs to Brazilian firm Gerdau, which according to company information is a leading producer of long steel in Americas.