The company claimed that the process will not release significant levels of carbon dioxide or other greenhouse gases above ground.

The mines, which are said to have 21 million tons of coal, were closed as per the Chinese government-mandated mine consolidation guidelines.

First phase of the project is planned to be completed in February 2015, and will yield a combined syngas output of 60,000m3 per hour.

On completion, the project will have an output of 880,000m3 of syngas per hour.

SinoCoking chairman and CEO Jianhua Lv said: "The production of this vast new quantity of syngas – a clean burning fuel – while preventing the escape of carbon dioxide and other greenhouse gases, is, we believe, a major technological accomplishment.

"Combined with the opening, next month, of our above ground syngas facility in Pingdingshan, this new project further establishes our company as one of China’s leading producers of clean energy products."