The accident occurred at 3 p.m. (0700 GMT) at the Shuangyang coal mine of Heilongjiang Longmei Shuangyashan Mining Co, and is initially believed to have been caused by a rock burst, the report said.

The cause of the accident is under further investigation, CCTV added. Rock bursts happen when pent up energy stored in rock causes it to violently fracture.

The report did not provide information on whether other people were still unaccounted for.

China's coal mines have seen a string of deadly accidents this year despite repeated government calls for stricter enforcement of safety standards, as miners seek to step up coal output.

(Reporting by Andrew Hayley; Editing by Edmund Klamann and Andrew Heavens)