The national environmental watchdog has removed the director monitoring investigation of pollution in the Tengger Desert having seen an improvement, the Beijing News reported on Sunday.

The Inner Mongolia autonomous region has invested more than 300 million yuan ($47 million) in building projects to treat pollutants since direct supervision by the Ministry of Environmental Protection began in May, the report said.

In addition, Ningxia Hui autonomous region has punished 15 officials held accountable for the pollution, it added.

In September's review, the ministry found improvement in the desert environment and strengthened monitoring conducted by provinces and city governments allowing it to remove the director, the statement said, adding that the cities must continue to monitor the environment.

More than 40 companies have been revealed to have been illegally discharging pollutants into the desert, contaminating the soil and underground water, based on reports since September last year.