People wear masks at Tian'anmen Square in Beijing on Monday, as smog returned to the city after a short time of relief.[Photo/China Daily]

Governments usually issue restrictions to reduce excessive emissions of pollutants, especially from industrial production, and limit the use of vehicles to reduce smog in northern regions in winter.

By Sunday, a total of 26 cities, including Shijiazhuang, have issued red alerts for the coming days, the highest in a four-tier warning system that involves the restriction of industrial production, according to the ministry.

But inspectors from the ministry and affected regions said they found many violations of restrictions, especially by small factories along the border regions of two provinces of Henan and Shandong, with a company in Shandong's Dezhou found to have resumed production before getting approval.

Such violations have long been an issue "which is closely related to companies' pursuit of profits," said Ma Yong, an environmental researcher with the Supreme People's Court Law Center, adding that the punishment for being caught violating regulations is not substantial enough.

In addition, some governments are hesitant to ban production as it plays a big role in local economic growth, Ma added.

"All violating companies will be punished severely, in accordance with the strictest standards," said Liu Bingjiang, head of air quality management at the ministry, adding that policy-makers who neglect their responsibilities in protecting the environment will be held accountable.

"We will make efforts to fully implement restrictions during the emergency response periods."