Authorities in the southwest China municipality of Chongqing are claiming success in the battle against its infamous smog after a long campaign for cleaner air.

The city has seen the annual number of hazy days more than halved to an average of 51 in the last four years from 110 previously, claim officials.

The city government reported the number of days with good air quality at 287 last year, compared with 187 in 2000.

The hazy weather was a frequent phenomenon because of the city's unique geographic conditions, said Mayor Wang Hongju.

Chongqing, situated at the junction of the Yangtze and Jialing Rivers, is flanked by mountains and also sits at the upper end of the Three Gorges Reservoir. It is also the most important industrial base in west China.

This has resulted in fog from the rivers accumulating with soot and dust discharged by industrial firms.

Wang said the improvement was a result of growing awareness of environmental protection in the city.

The city government had spent more than 50 billion yuan (US$6.25 billion) in financing ecological and environmental construction and protection projects since it became a municipality 10 years ago.

The "boilers revolution", begun in 2000, saw all medium-sized and small coal-fired boilers in urban districts adapted for clean fuels such as natural gas and electricity.

Because of the campaign, the city saw a drop of 76,000 tons in discharges of sulfur dioxide, plus a decrease of 35,000 tons in the discharges of dust in downtown areas each year.

The city also launched a "blue sky" plan in 2001 by remodeling cabs and public buses operating in downtown areas to slash exhaust emissions, and began to relocate heavy industrial polluters out of downtown areas in 2004.

Forty-nine industrial enterprises had been moved by late 2006.

Trees coverage in the city had risen from 20 percent 10 years ago to 32 percent.

Chongqing used to fall under the jurisdiction of Sichuan Province. On March 14, 1997, deputies to the fifth session of the eight National People's Congress voted to make it a municipality.

China has three other municipalities: Beijing, Shanghai and Tianjin.

(Xinhua News Agency March 15, 2007)