Water supplies to 200,000 people in Shuyang county of east China's Jiangsu Province have been halted for more than 40 hours after ammonia and azote polluted a local river.

The county government said it was unable to tell when supplies would resume because the environment watchdog was yet to pinpoint the source of the pollutants before measures could be taken to curb the spill.

Harmful substances were detected in the water at 3:00 pm on Monday and the level of 28 mg per cubic meter is about three times the upper limit for drinkable water.

"The tap water turned yellowish and smelly at 3:00 pm. Supplies were cut off after a while," said Li Jinping, a resident in Xuefu Community in the county proper.

A resident from neighboring Huayuan Community complained her house had had no tap water since midday Monday. "Except for a few drops of red, stinky water on Monday night," said Wang Yinzhen.

An initial investigation indicated the pollution could have been caused by industrial sewage from chemical plants on the upper reaches of the Xinyi River, which originates in Shandong Province.

The county government is seeking help from Shandong to trace the pollution source.

Meanwhile, it has arranged alternative water supplies from 33 unpolluted wells, a spokesman with the county government said.

He said the county had also diverted water from Hongze Lake into local water sources to dilute the pollutants.

Jiangsu suffered another water crisis at the end of May, when a severe blue-green algae outbreak left tap water undrinkable for a week for half of the 2.3 million residents in Wuxi city.

Barely two weeks after the water returned normal, satellite pictures captured on June 15 indicated another algae bloom spanning 800 square kilometers in the central-western and northern parts of the lake, causing wide-spread concern in cities along China's third largest fresh water lake.