More than 3,500 unlicensed polluters have been found in eight provincial-level regions, including Beijing, Tianjin, Shanxi and Shandong, since a pilot program was launched in March, said a senior environmental official on Friday.

"Many polluters are still not covered by environmental supervision," said Liu Zhiquan, an official in charge of environmental assessment and emissions control at the Ministry of Ecology and Environment, during a news conference.

The State Council, or China's Cabinet, published a revamped pollutant emissions policy in late 2016 requiring all stationary polluters, meaning polluting companies that have their production activities in fixed locations, to be covered by the pollutant emissions permit system by 2020. So far, about 51,000 pollutant emissions permits have been issued.

To have a clearer picture of all polluters, the ministry launched a pilot program in eight provincial-level regions in March, and found more than 3,500 unlicensed polluters in these regions.

Liu said these unlicensed polluters have been exerting huge "negative impact" on the environment in the regions and will cause harm to achievements made in environmental protection.

For those that have been granted pollutant emissions permits, many were found to have failed in monitoring pollutant discharge and reporting monitoring information to the authorities as required.

Local environmental authorities have also failed to adequately supervise these licensed polluters due to lack of technological capacity and the poor knowledge of law enforcement officers on relevant policies and standards.

Liu acknowledged that the country still faces challenges in fully implementing pollutant emissions permit policies. He added that the ministry will continue to crack down on polluters without emissions permits and those that do not follow the pollutant discharge limits according to their permits. Some cases will be made public in hope of deterring other polluters.