Shanghai city workers retrieved 369 bodies from the Huangpu River yesterday, bringing the municipality's total to 10,164 since the first carcass was found earlier this month.
Jiaxing in neighbouring Zhejiang province, whose farmers are accused by Shanghai of dumping the pigs into the river upstream, had found another 4,664 dead pigs, media reports said yesterday.
But the Xiao Xiang Morning Herald, based in the central province of Hunan, quoted residents of Xinfeng in Jiaxing as estimating more than 10,000 pigs had been recovered from the water there.
The carcasses have prompted health concerns about water contamination, and the pigs' cause of death.
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Authorities have assured the 23 million residents of the Shanghai urban area that the water supply, of which 20 per cent comes from the Huangpu River, is safe, but local residents remain worried about contamination.
Tests on water and food supplies had been intensified.
A local official was quoted by the Jiaxing Daily last week as saying the cause of the deaths was "complicated" but the number was "within the normal range" expected in such a large population.
Nore than 18,000 pigs died in January and February in Jiaxing's Zhulin village, where most of the 1,400 households breed pigs, the report said.
Authorities have also found traces of a common pig virus in some of the animals floating in the Huangpu River this week.
"Shanghai's animal control authority found 'porcine circovirus', a common disease among hogs that was not known to infect humans, in 13 of 20 samples of internal organs taken from dead pigs retrieved from the Huangpu," China's Ministry of Agricultural said in a statement.