A total of 371 high-polluting chemical and construction enterprises in Beijing have slowed or suspended production amid the most serious smog in recent years.

"Power, iron and steel, metallurgy, coking and cement industries and the heating system are key industries under inspection. Any violation will be severely punished," said Zhong Chonglei, leader of the inspection team from the Beijing Municipal Environmental Protection Bureau.

The bureau has sent inspectors to monitor the implementation of the suspension order.

Sinopec Beijing Yanshan Co started limiting its production on Sunday afternoon. A large part of its oil refining and chemical engineering units have been shut down, including nine sets of its main equipment and the butyl rubber production line.

By the end of Monday, the company's production was down by 30 percent, said Qu Hongliang, manager of the production section of the company.

"Our company's emissions were noticeably decreased. Normally our crude oil processing equipment can process 84,000 metric tons of oil every day. Now the volume has decreased to 26,000 tons per day," said Qu.

Volatile organic compounds, such as oxynitride and sulfur dioxide, have all shown remarkable decreases, Qu added.

Beijing Building Materials Group has suspended three of its four cement grinding mills.

As of Wednesday, about 2,100 polluting companies have reduced or suspended production.

"Beijing needs to upgrade its public transportation to guide people away from driving their own cars, which produces far too much emissions," said Wang Zifa, researcher in atmospheric studies at the China Academy of Sciences.

"Two main factors contributing to the heavy smog are automobile emissions and high-polluting enterprises such as iron and steel that are clustered in eastern China," Wang said.

"We need to strengthen control over emissions, not as a contingency plan but as a long-term and regular mission," said Zhang Jinliang, chief scientist at the environment and health innovation center of the Chinese Research Academy of Environmental Sciences.

yangziman@chinadaily.com.cn