All cement producers in Beijing are closed, so are more than 200 quarries and lime producers, all in an effort to improve air quality. Chemical and petrochemical plants also have to reduce emissions by 30 per cent. Some steel producers have to relocate to neighbouring provinces.

Bans in Hebei will cut power output by 745,000 kwh. They will reduce coke production by 350,000 tonnes, iron out put by 7.11 million tonnes as well as steel by 5.58 million tonnes and cement by 9.67 million tonnes.

It is not clear whether workers employed by companies forced to shut down will be paid and if so by whom.

Bans have also come into effect on companies that are located far from the capital like hundreds of coal-burning plants in Shanxi, Shandong and Inner Mongolia, already closed or threatened with closure because of excessive pollution.

China is also facing its worst power shortages in a long time, estimated by official sources to be around 16 million kwh ( 5 million in Guangdong alone), a situation that has forced many factories to scale down their activities.

More than 70 per cent of all power plants rely on coal whose price has doubled in the last few months. The government has however kept the price of electricity low so that power plants are operating at a loss and cutting back on coal reserves to reduce costs, or using low-grade coal which is more polluting.

They are hopeful though that the government will eventually raise prices but not before the Olympic Games at least.