A number of companies, including some State-owned enterprises, have been strongly warned about polluting emissions following recent surprise inspections from the Ministry of Ecology and Environment.

Minister Huang Runqiu and Vice-Minister Zhao Yingmin were among the heads of the inspection teams that visited cities that have experienced rebounds in air pollution in Henan and Shaanxi provinces, according to the ministry.

Falsifying monitoring data, abnormal operation of air pollution control facilities and nonobservance of the government's instructions for emergency air pollution reduction were some of the major violations that were found.

Henan was targeted because of a "grim situation for air pollution control", the ministry said in a media release on Wednesday.

"Since the end of 2022, long-lasting, cross-year smogs have occurred in vast areas in southern Henan. Some areas even consistently faced heavy and even more severe air pollution events," it said.

In a move to supervise and support local air pollution control work, the ministry said, Huang carried out surprise visits to seven companies in the cities of Pingdingshan and Xuchang in Henan from Monday to Tuesday, with six of them found to have outstanding violations.

Wuyang Steel in Pingdingshan, a State-owned company, was found to have been emitting waste gas directly without removing sulfur as required, it said. The company also neglected local authorities' demands to reduce emissions in the case of heavy haze.

According to Aiqicha, a financial information service provided by Baidu, China's largest search engine company, Wuyang Steel has been punished for environmental violations 11 times since 2017.

In an inspection by the local environmental authority in 2020, law enforcement officers found that 19 heavy-duty, diesel-powered trucks belonging to the company were not fitted with necessary emissions filters.

At Tianrui Coal Coking, also in Pingdingshan, inspectors from the ministry found heavy air pollution caused by waste gas leaks. The enterprise is suspected of having interfered with online monitoring facilities to cover up the violation.

Huang stressed maintaining "zero tolerance" in policing environmental violations, especially those involving collusion between emitters and third-party environmental monitoring companies to falsify data.

Such data falsification is "extremely vile in nature" and will result in an "extremely bad effect". "We must resolutely crack down on it," the minister said.

He also emphasized that State-owned companies should set good examples and standards in their sectors.

According to a release from the ministry on Friday, a team headed by Vice-Minister Zhao visited some companies unannounced in Xianyang, Weinan and Hancheng in Shaanxi from Tuesday to Wednesday, and found violations at four of them.

At Hancheng Yulong Coking, inspectors found the company diluted waste gas passing through the automated monitoring apparatus to interfere with the facility's operation, it said.

In Xianyang, Shaanxi Heli Thermal Insulation Material Products was found to have cut off a pipe used for collecting waste gas samples.

The ministry has asked local environmental authorities to further investigate the violations. "Those prominent violations concerning data falsification and modification should be transferred to public security organs for handling," it said.

Companies that fail to remedy air pollution violations after receiving warnings face heavy fines and could even be shut down.