BEIJING, Feb. 7 (Xinhua) -- Beijing plans to issue pollution alerts that will warn residents to avoid certain areas of the city on days when the air is heavily polluted, said the environment protection bureau.

    The city also intends to close factories and construction sites when the air becomes heavily polluted, said an official with the municipal environment protection bureau on Wednesday.

    Shi Hanmin, director of the municipal environment protection bureau, said that more needs to be done to improve the air quality of Beijing, which is still below national standards, short of commitments made in its Olympic bid and not up to the expectations of residents.

    The municipality had 241 'blue sky days' in 2006, exceeding the government's target by three days.

    This year the target is 245 blue sky days. "We are faced with a very hazardous environmental situation," said Shi.

    Sulfur dioxide emissions dropped 7.9 percent in Beijing last year, while the municipal GDP grew by 12 percent in 2006.

    Beijing launched the "Defending the Blue Sky" program in 1998, when the city had only about 100 days of 'blue sky' days. Since then, air quality has improved for eight straight years, due to measures taken by the environment watchdog and the "mercy of nature".

    Beijing has taken the lead in China and imposed Euro-III car emission standards, but exhaust fumes emitted by its 2.8 million motor vehicles, including two million private cars, remains one of the primary sources of pollution in the capital.

    Shi told Xinhua that 300,000 high-emission vehicles will be taken off the roads in 2007.