An excess level of ammonia-nitrogen has been found in drinking water supplies of more than 300,000 people in Wuhan, capital of central China's Hubei Province on Wednesday, local authorities said. 

Two major water suppliers in the city have halted water production.

The Baihezui and Yushidun water plants in Wuhan suspended water production at around 4 p.m. and 7 p.m. respectively, after tests showed that the Wuhan section of the Han River, a major tributary of the Yangtze River, contained excessive amount of ammonia and nitrogen, the city government said in a statement.

Their moratorium of water supplies has caused a water shortage in an area of 260 square km in the city, affecting hundreds of food manufacturers as well as the livelihood of local people, according to the statement.

As of 9 p.m., water supplies in the city had been up to standard, the statement said. Local departments are testing the river water every hour, while environmental protection bureaus on the provincial and city levels are investigating the source of the pollution, it added.

(Xinhua contributed to the story)