No mass swine epidemic had broken out in Jiaxing after the city became a suspected source of dead pigs floating in a river upstream from Shanghai, officials said Tuesday.

A total of 2,800 pig carcasses had been fished out from Huangpu River as of Sunday evening, Shanghai municipal authorities said, adding that some corpses carried labels indicating they came from Jiaxing in the neighbouring province of Zhejiang.

The river is a major drinking water source to Shanghai, an eastern metropolis of 23 million people.

Shanghai authorities said water quality in the city has not been affected.

A statement from the agriculture department of Zhejiang said no signs of an epidemic were found in Jiaxing. The death rate of local hogs was normal, said Jiang Hao, vice head of the animal husbandry bureau of Jiaxing.

But Jiaxing authorities admitted the dumping of the dead animals by local pig farms.

Most hog producers in Jiaxing are small, family-run farms. Lacking legal awareness, some farmers freely disposed of their pig carcasses, said Yu Hongwei, vice head of the environment protection bureau of Jiaxing.

According to a report on the March 6 edition of Jiaxing Daily, dumping of dead pigs in rivers is common among Jiaxing villagers due to over expansion of the hog industry and a lack of burial sites.

"Some 40 to 50 floating pigs ended up near the Wansheng Bridge, and there was a strong stench there," it said, citing a Jiaxing Daily reporter who was in Pinghu City under the jurisdiction of Jiaxing.

Yu said Jiaxing had organized to collect and dispose of the carcasses by burial or cremation and had tracked down the farms responsible for causing the pollution.