Nearly 3,000 dead pigs have been found floating in Shanghai's main waterway, the Chinese city's government said Monday as residents expressed fears over possible contamination of drinking water.

Shanghai's water bureau said over the last two days workers had fished 2,813 pigs out of the Huangpu river, which cuts through the commercial hub and creates its waterfront Bund district.

In the southwestern district of Songjiang Monday, workers used long-handled rakes to pull the bloated animal carcasses, which were turning from pink to grey, out of the water onto a small boat, an AFP photographer witnessed.

The stench of rotting pork hung over the river as workers dumped the partially disintegrating bodies into the hold.

The dead pigs included both piglets and adults weighing hundreds of pounds, the Shanghai city government said.

Reports said the first bodies were discovered Thursday and the pigs probably came from the adjoining upstream province of Zhejiang, where farmers were believed to have dumped them in the river after they died of disease.

"Is the water still drinkable after dead pigs were found floating in it?" Shanghai resident Liu Wanqing was quoted as saying by the China Daily newspaper.

"The government has a responsibility to conduct a thorough investigation and provide safe water to residents."

The affected portion of the river accounts for more than 20 percent of the raw water supply to the city's 23 million people, according to the water bureau.

The Shanghai government said it was testing samples from the river on an hourly basis and so far all indicators were "normal".

A total of 12 boats had been deployed to fish the dead hogs out of the water, the Global Times newspaper said, as experts warned of mounting danger to the water supply from rotting animals.

Separately, Shanghai's agricultural commission said some of the pigs had tested positive for porcine circovirus, which it described as a common swine disease that does not affect humans.