Beijing  - China on Friday said it would restrict usage of vehicles before and during the Beijing Olympics to improve air quality and allow better traffic flow for visitors.

All private vehicles will be limited to alternate-day usage from July 20 to September 20, based on licence plates ending in odd and even numbers, the government said.

Taxis, buses and emergency vehicles are exempt from the restrictions, while about 70 per cent of government vehicles are expected to be kept off Beijing's roads.

The restrictions are designed to improve traffic circulation and raise air quality for the Olympics in August and the Paralympics in September, the Beijing city government said in a statement.

The traffic control measures are expected to remove a daily average of about one-third of the city's 3.3 million vehicles.

The statement said many heavy trucks and all vehicles which do not meet the European number one emissions standard will be banned throughout the period.

The government will exempt all Beijing vehicle owners from road tax for the three months in compensation for the temporary restrictions, costing it 1.3 billion yuan (186 million dollars) in lost revenue.

China earlier said it planned controls on industrial pollution and suspended dust particles to improve Beijing's air quality during the Olympics.

The city will ban all excavations and concrete pouring at construction sites from July 20 until September 20, Du Shaozhong, deputy director of the Beijing Environmental Protection Bureau, told reporters recently.

It will shut down inefficient coal boilers, stop work at quarries, cement and concrete plants around Beijing, and has ordered 19 heavy-polluting firms in the city to cut emissions by an extra 30 per cent in the three-month period, Du said.

Contingency plans for the Olympic competition days in August include tougher "urgent control measures" to be used if Beijing experiences "extremely negative atmospheric conditions", he said.

The International Olympic Committee said it would also have contingency plans for the possible rescheduling of cycling, distance running and other events demanding high respiratory function for more than an hour, depending on pollution and other factors such as heat, humidity and wind. (dpa)