The TV station in Yingde, a city of 1.06 million people, broadcast a warning Tuesday evening telling residents not to drink the tap water due to toxic contamination in the upper reaches of the river, Xinhua news agency said.

Quoting the local government, Xinhua said the slick threatened water safety for about 100,000 urban residents of Yingde along the lower reaches of the river.

The river, which runs into the Zhujiang or Pearl River that flows through the main southern city of Guangzhou, is a major source of drinking water for cities in the north of Guangdong province, it said.

Guangdong provincial environment protection department found the slick was caused by an excessive discharge of waste from a state-owned smelting works in Shaoguan, located 90 kilometres (55 miles) north of Yingde, Xinhua said.

Waste discharges had increased the volume of cadmium in the river at Shaoguan to nearly 10 times above safety levels, "seriously endangering" the safety of water downstream, the department found.

The smeltery had halted operations and closed the waste water outlet blamed for the discharge, according to the Shaoguan environmental protection office, Xinhua said.

The toxic slick was moving slowly towards Yingde and was due to reach the city in "two or three days", it said.

The Guangdong provincial government has decided to discharge water from reservoirs in the upper reaches of the river to dilute the pollution, Xinhua said, quoting experts whom it said arrived in Yingde on Sunday. It did not say when the discharge occurred.

"We suggested to discharge more than 70 million cubic meters of water from a reservoir and the diluted water will be safe enough to drink," it quoted an expert who declined to give his name as saying.

Yingde was building a line to send clean water from a reservoir to the urban area, which is home to more than 100,000 people, Xinhua said.

Water carriers, including 15 fire engines, have also been put into service to ferry drinking water, it said.

Provincial and environmental protection officials were investigating the incident which follows a massive toxic spill in northeast China last month.

A PetroChina chemical plant in Jilin province exploded in mid-November, causing a large amount of toxic benzene and nitrobenzene to spill into the Songhua River.

The spill forced officials to cut off water supply for days to millions of people in Harbin and other cities in neighboring Heilongjiang province, which depends on the Songhua River for water.

The poisonous slick entered the Amur River in Russia, which shares a border with Heilongjiang province, on Friday.

Many factories in China are located on river banks as they need water in their production process and often discharge industrial wastes into the rivers, causing most of China's rivers to be polluted.

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