China's environment ministry has named and shamed several cities in the north of the country for not doing enough to cope with smog, state news agency Xinhua reported.

Large parts of northern China have been blanketed in choking smog this winter, defying repeated government efforts to tackle the problem.

Pollution alerts are common in northern China, especially during bitterly cold winters when energy demand, much of it met by coal, soars.

The ministry's inspection of 18 cities in Beijing, Tianjin and Hebei province found several problems in their smog response, including inadequate planning and poor implementation of policies, Xinhua said late on Sunday.

Hebei's Cangzhou city was criticised for failing to draw up a detailed list for business shutdowns on heavily polluted days, which made it hard to achieve a reduction in emissions, the report said.

Jiaozuo city did not begin traffic controls taking vehicles off the road when the city went on red alert for pollution, while Baoding city was well behind in upgrade coal-fired boilers to make emissions cleaner, it added.

China is in the third year of a war on pollution aimed at reversing the damage done to its skies, soil and water after decades of untrammelled economic growth. But measures taken so far have had little or no effect.