Law enforcement officers dispatched by China's top environmental protection agency spotted a wide range of violations in Beijing, Tianjin and neighboring Hebei province in the latest round of inspections.

A total of 2,690 cases involving air pollution control law violations were spotted by 200 inspection teams dispatched by the Ministry of Ecology and Environment in the area from June 11 to 24, the ministry said on Friday.

These included 355 failed attempts by local authorities to shut down or upgrade high-emission enterprises, and 660 cases of enterprises discharging industrial dust into the air without proper treatment, it said.

Other problems include factories failing to install pollution-control facilities or failing to operate them, and construction sites or open mines failing to take proper measures to reduce emissions.

The ministry will supervise local governments or enterprises as they carry out the required corrections, it said.

The "blue sky" campaign, launched by the ministry on June 11, will last until April 28, and intensified supervision will extend from Beijing, Tianjin and neighboring Hebei province to 11 cities in other parts of China, including in Shanxi and Shaanxi provinces in August, and to the Yangtze River Delta in East China in winter, according to Tian Weiyong, chief for environmental supervision at the ministry.

"Supervision teams will be dispatched to every county in these areas, and by winter this year about 1,000 inspectors will be working in all 80 cities in these areas to fight air pollution," he said.

Beijing, Tianjin and much of Hebei province is one of the regions with the most serious air pollution in China. Peak seasons for pollution usually occur with the approach of winter in November, due to increased consumption of coal for heating in North China.

A key task for air pollution control in the area in the winter will be discouraging individual households from burning coal for heating, and using cleaner fuels instead, he said.

The ministry estimates an additional two to three million households in the area will switch to gas or electricity, Tian said.

Despite increases in public awareness for environmental protection, China still faces severe challenges in environmental protection, and environmental law enforcement needs to keep intensifying, he said.

In some places, inspectors dispatched by the ministry earlier this month have found enterprises that failed to rectify problems as required, and in some cases local governments even took measures to help the enterprises conceal pollution for local economic development, according to the ministry.