Chengdu, the capital of southwestern China's Sichuan Province, was forced to cut its major tap water supply yesterday because one of the city's major drinking water sources was polluted.

The supply was cut at 6pm and affected most of Chengdu's 12 million people, with many forced to carry water from public taps at street level or buy bottled water at dinner time.

An unnamed source from the Chengdu Water Corporation said garbage was dumped in the Baimu River, a major drinking water source, upstream from downtown in the city's Chongyi Township.

He said the pollution was not severe but the tap water services for most downtown residents were turned off when they found the water began to smell, according to a local radio station.

The water corporation said the water services will be back at about 11pm. It said the pollution has been alleviated, but it was double-checking the water quality to ensure safety.

According to a local Internet forum, only ground floor apartments had any water and that was a weak flow. The water corporation said this water was safe.

It was still unknown as to what kind of pollution it was and who dumped the garbage.

Last July, Chengdu's tap water supply was cut because heavy rains flooded the Minjiang River, another drinking water source, and silted up many water plants.

Industrial pollution has caused more trouble to other big cities along China's major rivers.

Last year heavy pollution turned portions of the Hanjiang River, a branch of the Yangtze in central China's Hubei Province, red and foamy, forcing the government to cut water supply to as many as 200,000 people.

In 2005 carcinogenic chemicals including benzene spilled into the Songhua River. The northeastern city of Harbin cut water supplies to 3.8 million people for five days.