BEIJING, Aug 30 (Reuters) - More than half China's 1.3 billion population, including 278 cities, live without any form of sewage treatment, state media said on Friday, quoting city planning officials.

And eight of those cities have populations of more than 500,000, Zhao Baojiang, chairman of the China association of city planning, was quoted as saying.

In its rapid development into the world's fourth-largest economy, China has been struggling to curb horrific water and air pollution.

It has become the world's top emitter of acid-rain causing sulphur dioxide and many analysts expect it to overtake the United States this year as the biggest greenhouse gas emitter.

An estimated 5,000 "administrative towns" and 20,000 smaller, market towns also had no sewage treatment facilities and a lack of clean water was especially acute in the central province of Henan, the China Daily said.

Pollution has taken on greater urgency as Beijing tries to clean up its notoriously filthy air before hosting the 2008 Olympics next August.

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