NANNING - A cadmium pollution belt that has wreaked havoc in a South China river for two weeks will not result in the cutting of water supplies to a downstream city, a local environmental protection official said Tuesday.

"After two weeks of cleanup, the pollution is under control and we are certain it won't affect tap water supplies in Liuzhou city or other downstream areas," said Feng Zhennian, an official with the environmental protection department of Guangxi Zhuang Autonomous Region.

Feng, who is also spokesman for an emergency response center set up to handle the incident, made the remark at a press briefing Tuesday afternoon.

"The regional government has launched an overhaul on all heavy metal firms as it hopes to halt pollution discharges," he said.

Lab analysis on Tuesday showed the cadmium concentration levels near Liuzhou's water plant were around two times higher than the official limit of 0.005 milligrams per liter, indicating the pollution was under control, said Feng.

As of 6 am Tuesday, drinking water produced by four major water plants in Liuzhou was up to standard, with cadmium concentrations no higher than 0.00065 milligrams per liter, according to the latest water quality tests.

When pollutants were first detected in the Longjiang River on January 15, however, cadmium concentration near the Lalang Reservoir -- where the pollution first leaked into -- was 80 times higher.

The source of the pollution was reportedly contained Saturday, as cadmium concentration at the Lalang Reservoir had returned to normal. But the pollutants have been flowing downstream and threatened water security in Liuzhou, a city with 1.5 million permanent residents in the city proper.

Feng's emergency response center estimated the contaminants totaled 20 tonnes in the Longjiang River and stretched 300 km in the downstream Liujiang River.

While the cause of the pollution is still under investigation, seven chemical plants executives have been detained on suspicion of industrial waste discharges.

The ongoing overhaul involves all heavy metal firms, including storage battery makers, leather producers and chemical plants.

Cadmium is a carcinogenic chemical mostly found in industrial effluents.