BEIJING: Beijing will ban half of its 3.4 million cars from the roads during periods of very heavy pollution, a state news report said on Friday.

The city will temporarily reinstate measures it introduced during the Olympic Games and ban cars on alternate days, depending on whether their license plates are odd or even, if pollution levels rise to extreme levels, the China Daily newspaper said.

``To protect public health over the long term, we must use both methods that increase the number of good air quality days and more stringent measures for when conditions are extremely unfavorable,'' the deputy director of the city's environmental protection bureau, Du Shaozhong, was quoted as saying.

Work would also be suspended at construction sites and high-polluting factories during extremely polluted periods, the newspaper said.

The restrictions will only be imposed if the air pollution index reaches 300, a threshold far above the city's normal air quality level, it said.

The driving restrictions imposed during the Olympic Games allowed Beijing's 17 million residents to enjoy clear blue summer skies as the city recorded its lowest August pollution levels in 10 years.

Since then, there have been calls in newspaper editorials for an extension of the Olympic traffic measures.

Last month, Beijing officials announced they would introduce some traffic restrictions for a six-month trial period.

At the start of October, city officials took nearly a third of government vehicles off the road. Starting next week, the remaining government cars, together with privately owned vehicles, will be banned from roads one day a week on a rotation basis according to license plate numbers. The rules do not apply on weekends and are to continue through February.

Thursday's pollution level was 47. Levels of 51-100 are considered moderate pollution, and anything over 100 is harmful to susceptible groups, including children and the elderly.

During the Olympics, the level dropped as low as 17 after registering nearly 100 just a day before the opening ceremony, according to the government.