The leak took place at about 9am local time on Dec. 24 in the Ganglu Iron and Steel company in Zunhua City under the administration of Tangshan, about 150km east of Beijing.

A total of 44 people were working around the blast furnace at the time of the leak. Two workers died instantly and five more succumbed to injuries in hospital soon after, State-run Xinhua news agency reported.

Ten other workers who were seriously injured died in the afternoon after emergency operation failed. Four of the 27 injured were released from hospitals. The others are still being treated at different local hospitals and are in stable condition. The workers were believed to be poisoned by carbon monoxide that emanated from the blast furnace.

Officials of Tangshan Work Safety Administration are still investigating the accident and have ordered local companies to conduct thorough safety checks.

The Ganglu company has about 7,000 employees. It has an annual output of 3 million tonnes of steel products.