Southern boomtown Shenzhen came third for "its role as the pioneer of China's opening up and reform policies", while glitzy Shanghai got fourth place "for being the country's financial centre", the official China Daily reported.

Institute chairman Gui Qiangfang said the assessment took into consideration Beijing's design, infrastructure, architecture, culture and natural beauty.

"Factors including the preservation of historical monuments, forest coverage, air quality, the transportation network, city life, public space and GDP were also considered," the newspaper said, with no hint of irony.

The result might come as a surprise to many visitors to China, home to clean and leafy cities such as Qingdao and Hangzhou in the east and the picturesque walled ancient capital of Xi'an in the north.

Historic sites in Beijing, often clouded by a toxic mix of construction dust, car fumes and factory emissions, have long been under threat, but the situation has become still more dire as the city is feverishly refurbished for next year's Olympics.

The ruling Communist Party ordered the confiscation of many ancient buildings to accommodate new state organs after it took power in 1949. Most of Beijing's ancient city walls were also destroyed in the first years of Communist rule.