The accident happened during maintenance at a pellet desulphurisation facility that belongs to the steelmaker and operated by Guoshun Group, according to the statement.

Local government is still investigating the cause of the incident, the authority said, without saying whether production and operation at the project have been halted. The project has pellet capacity of five million tonnes per year, according to the statement.

Bao Gang United Steel did not answer Reuters' call seeking comment. Guoshun Group declined to comment.

State-backed Bao Gang has an annual steel capacity of over 15 million tonnes per year, according to the company's website.

(Reporting by Min Zhang and Dominique Patton; Editing by Kenneth Maxwell)