Authorities in Jiaxing, Zhejiang province, denied a rumor saying that a large-scale pig epidemic had happened in the city.
"No abnormal animal epidemic was reported in Jiaxing," Jiang Hao, the vice-head of Jiaxing's veterinarian department said on Tuesday at a media conference.
He said local authorities are assisting Shanghai's veterinary departments with the investigations on the dead pigs that appeared floating on the Huangpu River.
Starting last week, dozens of dead pigs were found floating in the upper Songjiang section of the Huangpu River.
Shanghai authorities said on Monday that from the animals' ear tags they have so far determined the pigs came from Jiaxing. Tests have revealed that some pigs may have died from porcine circovirus, a common pig disease in recent years.
Chinese media reported that a large number of pigs had died in Jiaxing in the first two months of the year.
According to the Jiaxing Daily, in Jiaxing's Zhulin village, which depends on pig farming, almost all of the more than 1,400 households keep pigs. In January, 10,078 pigs died there and in February another 8,325 died.
Pigs in the area generally live in overcrowded pens where bacteria can breed easily. Consequently, many became sick and died, said the report, adding that there is not enough land to bury the carcasses.
Jiang said the authenticity and accuracy of the media reports remain to be proven. He didn't provide the number of dead pigs in the past two months.
He said that about 7 million pigs are raised each year in Jiaxing, and that most are raised by local villagers individually. The death rate of the animals is at a normal level of less than three percent.
Jiang added that Jiaxing has 600 non-hazardous treatment stations for dead pigs, and that farmers who hand over dead pigs will receive an 80 yuan ($12.75) subsidy for each carcass.
He admitted that some individual farmers had disposed of the carcasses directly because they believed that the "dead pigs are very unlucky".
By Monday, 3,323 carcasses had been retrieved from the river, according to Shanghai agriculture authorities.
The retrieved dead pigs have been sent for hazard-free treatment. They were buried in seven-meter-deep holes, and covered with at least three meters of thick soil. Some carcasses were also incinerated.