High-level environmental protection inspectors have filed 134 cases against companies in North China's Beijing-Tianjin-Hebei region over air pollution as part of an ongoing campaign to catch rule-breaking businesses.

About 200 supervision teams have been sent to the region, with the focus on steel, coal-fired power plants and construction industries, according to Li Ganjie, the minister of ecology and environment.

"The campaign is a long-term mechanism rather than a short-term movement, which aims at helping local governments solve their pollution problems and improve the environment," he said on Sunday.

The ministry said on Sunday that teams had checked 1,254 companies in Beijing, Tianjin and Hebei province, as well as surrounding areas, and discovered three companies that failed to meet air pollution standards.

In Hebei, North China's Shanxi province and Central China's Henan province and Tianjin, a total of 13 companies failed to meet the anti-air pollution installation standards, and 11 industrial companies' anti-air pollution facilities were not in working condition.

The ministry also announced one excessive pollutants discharge case in Shijiazhuang, Hebei province, and 35 construction fugitive dust emissions in Hebei and Shanxi.

The ministry has handed over all the cases to local governments, which will deal with the involved companies and individuals according to laws and regulations.

The ministry started the environmental protection campaign to strengthen the supervision against illegal pollution on June 11. It focuses on areas that include the Beijing-Tianjin-Hebei region, the Fenhe-Weihe plain in North China and the Yangtze River Delta region.

The number of days in a year with good air quality in Hebei, Shanxi and Henan, and East China's Shandong province and Tianjin is less than 60 percent, the ministry said.

The campaign will last till April 28. During the campaign period, the ministry will examine several times the cities involved and help local governments improve their industrial, energy and transportation structures and land use.

The ministry gained experience in this during an environmental protection campaign in the Beijing-Tianjin-Hebei region between 2017 to 2018. It will make full use of that experience in the enlarged area for the new campaign this year to 2019.