The companies include 66 steel makers, as well as coke plants, cement firms and small power generators, a government official in Tangshan said yesterday.

The companies would have to undergo strict environmental protection checks before they can resume production at an unspecified date.

Those ordered to halt production are small companies, and their impact on Hebei's steel industry, which accounts for about 20 per cent of steel production capacity in China, would not be significant, analysts said.

'It is hard to estimate how much steel production capacity would be shut down because most of the firms are very small ones,' said steel sector analyst Hu Yanping of industry portal Umetal.com.

Beijing, one of the most polluted cities in the world, has spent 140 billion yuan (S$28 billion) to combat chronic pollution as it prepares for the Summer Olympics, which open on Aug 8.

Pollution is a major concern for many athletes.

International Olympic Committee chief Jacques Rogge has warned that endurance events, such as the marathon, may be postponed if the pollution is too severe during the Games.

Vehicles that fail to meet emissions standards have been banned from entering downtown Beijing from Tuesday until Sept 20.

And from July 20, Beijing will launch a traffic control system to take half of the city's three million cars off the road, using an odd-even licence plate system.

Also, 70 per cent of all government cars and vehicles owned by state-run enterprises will be banned from the roads for two months from July 20.

Beijing residents have been urged to work from home and businesses asked to stagger their operating hours.

'As a lot of Olympic competitions will be held at night, we will urge companies to stop work early so that crowds going to matches are not travelling at the same time as people getting off work,' traffic official Zhou Zhengyu told the Beijing News.

On Tuesday, China closed several small corn starch makers in cities hosting events for the Games to fight pollution.

The Beijing municipal government issued rules in April ordering industrial concerns such as Shougang Group, one of China's major steel producers, to reduce or stop production from July 20.

Some producers on the list have already stopped work. Qinchang Glass, in Beijing's suburbs, has closed its plant, a company official said.

The Games received a boost yesterday with the White House saying that President George W. Bush will attend the opening ceremony. French media also reported that President Nicholas Sarkozy will be in Beijing, despite protests from human rights groups which demand that he boycott the Games.

REUTERS, AGENCE FRANCE-PRESSE