The cities of Guangzhou, close to Hong Kong, and Foshan had been put on alert over the spill of cadmium from a smelting works that has been flowing down the Beijiang river, China's second environmental crisis in weeks.

Officials on Wednesday ordered the gates of a dam to be lowered to help block the slick, and also released water from reservoirs into the flow to dilute the amount of the chemical.

"By releasing water from three reservoirs to dilute the pollution, the cadmium level will meet safe levels by the time the water reaches Guangzhou city," said a spokesman surnamed Xiao at the government information office in Guangdong province.

"There's no stoppage of water supply anywhere," the spokesman told AFP.

The density of cadmium kept dropping as a result of the measures, Xinhua news agency quoted environmental protection experts saying.

The water supply for Guangzhou, which has 10 million residents, comes from at least two other rivers. The city has more water than it needs, the Guangzhou Daily newspaper said on Thursday, citing a Guangzhou city government notice.

The toxic slick was caused by an excessive discharge of cadmium from a state-owned smelting works in Shaoguan city into Beijiang, a river that is a major source of drinking water for cities in the northern part of Guangdong.

The Beijiang runs into the Pearl river, which flows through Guangzhou.

The waste discharge increased the volume of cadmium in the Beijiang to nearly 10 times above safety levels, "seriously endangering" the safety of water downstream, Xinhua had cited the local government saying.

The discharge occurred on December 15, according to state media, but was not reported until this week.

The slick on Thursday was still at a part of the river in northern Yingde city, about 180 kilometers (110 miles) upstream from Guangzhou.

Officials in Yingde, a city with a population of one million some 90 kilometers (55 miles) downstream from the smelting works, told AFP on Wednesday that the lowered dam gate was blocking the slick from flowing to the part of the river that supplies water to Yingde's urban areas.

They were working around the clock to build a 1.4 kilometer pipeline to divert clean water from a local reservoir, to provide potable water to the 100,000 residents there. The project would take 48 hours, an official from Yingde's Water Resources Bureau said at the time.

A Yingde city official had said the city was confident it would not need to cut off water.

The incident recalled a chemical spill in a river in northeast China after a benzene plant explosion last month that left millions without water for four days.

That spill was headed to the Russian city of Khabarovsk along the Amur river and predicted to hit the city of 600,000 on Thursday.

The environmental disasters have highlighted the seriousness of water pollution in China and raised questions about Beijing's ability to handle its rapid pace of development.

Cadmium is used in protective plating. Serious exposure can cause problems including bone fractures, reproductive failure and damage to the immune and central nervous systems.

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