GUANGZHOU/NANNING - Government authorities of Fengkai County, South China's Guangdong province, on Saturday warned that water in a section of the Hejiang River has been tainted by pollution upriver.

An initial investigation suggests that the pollutants are thallium and cadmium, the county's publicity department said in a statement.

According to the department, dead fish were found in a section of the river in Fengkai County around 6 a.m. Saturday after hazardous substances had been detected upstream in neighboring Guangxi Zhuang Autonomous Region.

Sample examination indicated that the density of thallium was 0.00022 milligram per liter, or 1.2 times of the allowed maximum level, while the density of cadmium was 0.0034 milligram per liter, a level that makes the water second degree.

Both thallium and cadmium are toxic to human beings.

The county government has warned the local tap water plant and residents against taking water or eating aquatic products from the Hejiang River, a main tributary of Xijiang River. Xijiang River is a trunk of the Pearl River which forms major water source for Guangdong and neighboring Hong Kong and Macao special administrative regions.

Life at Fengkai County remained largely undisturbed, although some residents began to store bottled water for fear of drinking water shortage.

It is estimated that 35,000 people in the townships along the Xijiang River would be affected.

No casualties have been reported in Guangdong or Guangxi so far.

The government of Guangxi has started an emergency response to ensure safe water supply along the Hejiang River and its downstream regions.

A further investigation is under way to determine the source of the pollutants.