On Tuesday, the Ministry of Environmental Protection summoned officials from Heilongjiang's four major cities - Harbin, Jiamusi, Shuangyashan and Hegang - and its Commission of Rural Affairs to Beijing, urging them to vigorously take up the task of preventing pollution in winter.

The ministry also notified them of their poor or unsatisfactory performance in environmental protection in past months.

In September, the ministry conveyed to the officials the desire of the central government to reduce air pollution in Heilongjiang, but it did not achieve clear results.