BEIJING -- More than half of the Chinese cities monitored by the Ministry of Environmental Protection, especially those in northern China, reported air pollution Wednesday.

About 57.8 percent of Chinese cities monitored by the ministry, including Beijing, reported varying degrees of air pollution, Wednesday morning, according to real-time data on the ministry's website.

Of the 338 cities monitored by the ministry, 7.1 percent, including Shijiazhuang the capital city of Hebei Province, which neighbors Beijing, reported serious air pollution, with air quality index (AQI) readings exceeding 300 as of Wednesday.

Another 12.8 percent of these cities, including the northern metropolitan Tianjin, were experiencing heavily polluted air, with AQI readings between 201 and 300, said the ministry.

Moreover, the air in 9.8 percent of cities, including Beijing, was moderately polluted, with AQI readings between 151 and 200.

The data also revealed 28.1 percent of the cities, including Changchun in northeastern Jilin Province, had slightly polluted air, with AQI readings between 101 and 150.

PM 2.5, particulate matters with a diameter smaller than 2.5 micrometers, was the primary pollutant in most of the cities, the data showed.

Due to unfavorable pollutant dispersing conditions, the ministry said air pollution in most regions was not expected to improve until Thursday night.

Many Chinese cities suffer from winter smog, triggering public concern.

The authorities have stepped up efforts to cut outdated production capacity and have dispatched inspection teams to provincial areas to supervise environmental measures taken by industrial firms.