China has ordered the closure of 40 factories in a city close to Beijing in the run-up to the Olympics Games.
The plants in the eastern port city of Tianjin have been ordered to stop production from late July.
The move is the latest attempt by China to minimise air pollution in the capital during the Games in August.
Some athletes have expressed concern about air quality affecting their performance and damaging their health.
State media reports that work on key building sites in Tianjin will be suspended, including the construction of an underground railway line.
Two cement works, 26 building sites and six factories which cause "effluvial contamination" will also be affected, said Xinhua news agency.
On Friday, similar action was taken in the city of Tangshan, 150 km (90 miles) east of Beijing where about 300 factories will suspend their operations.
Beijing is one of the most polluted cities in the world and officials have been making extensive efforts to improve air quality before the Games.
But correspondents say that pollution in the city is as bad as ever and it is often shrouded in heavy smog.