Chen Jining, minister of environmental protection, answers questions at a press conference during the fifth session of the 12th National People's Congress (NPC) in Beijing, Mar 9, 2017.?[Photo by Feng Yongbin/chinadaily.com.cn]

Curbing winter smog in the north is now the biggest priority - and challenge - for China's efforts to improve air quality, according to the Ministry of Environmental Protection.

Data on the levels of PM2.5, tiny hazardous particulate matter, show the air quality in regions such as the Yangtze River Delta and the Pearl River Delta has improved by at least 20 percent over the past three winters, Chen Jining, minister of environmental protection, said during the ongoing annual session of the National People's Congress.

By contrast, the air quality in the Beijing-Tianjin-Hebei region has improved only by 9.6 percent over the same period, he said.

Chen said air pollution control measures are proving effective, but he added that it will be hard to eliminate severe smog within two or three years.

"However, we're confident we can solve the problem faster than developed countries did," he said.