The Ministry of Agriculture has launched an urgent investigation into the deaths of more than 3,000 pigs whose carcasses ended up in East China's Huangpu River.

The probe will also involve animal epidemic protection departments in Shanghai and Zhejiang province, said Chen Xiaohua, vice-minister of agriculture.

Officials first started receiving calls about dead pigs in the upper Songjiang section of the river last week.

By Monday, 3,323 carcasses had been retrieved, according to Chinese news portal xinmin.cn.

Initial investigations have found no evidence of widespread animal disease in the immediate area, Chen said on Monday, although tests have revealed some pigs may have died from porcine circovirus, a disease common in pigs in recent years.

Shanghai authorities said that from the animals' ear tags they have so far determined the pigs came from Jiaxing in Zhejiang province.

Shanghai's Agriculture Committee said it has been in contact with animal departments in Zhejiang and the agriculture department of Jiaxing, and has sent officials to ask local departments to take appropriate measures.

Some Chinese media, including Jiaxing Daily, reported that a large number of pigs had died in Jiaxing in the first two months of this year.

In Jiaxing's village of Zhulin, which is dependent 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 8,326 died, Jiaxing Daily reported.

Pigs in the area generally live in overcrowded pens where bacteria can breed easily. Consequently, many became sick and died, said the report, adding there is not enough land to bury the carcasses.

A spokesman for the Jiaxing government named Hu said the city has procedures for collecting dead livestock.

"Farmers are required to hand over dead animals to designated departments or collection stations for disposal," he said.

But he added, "We can't rule out the possibility that some farmers have simply thrown the pigs away."

Tests revealed some dead pigs may have died from porcine circovirus, according to Shanghai Agriculture Committee on Monday.

The Shanghai Animal Diseases Control and Prevention Center collected five samples from the dead pigs, including from their hearts, livers, spleens, lungs, lymph nodes and tonsils to test for viral pathogens.

The virus cannot affect humans, the committee said.

Hu also said no animal epidemic had been reported in Jiaxing.

"Agriculture departments are still investigating, and the result will be released on Tuesday," he said.

Shanghai environmental and water departments are keeping a close watch on the water quality, and have increased patrols on the river.

The quality of water from the upper reaches of the Huangpu River was reported as stable and was unchanged from last year, officials said.

Water from plants in Songjiang, Jinshan, Minhang and Fengxian also met national standards, the Shanghai government added.

The recovery of the pig carcasses continues, authorities said.

Chen said the incident highlighted that various measures need to be strengthened and improved.

He added that it was also necessary to improve the levels of health and environmental education among farmers, suggesting there should be a system of rewards and subsidies for those implementing the safe treatment of dead animals.

When a problem is identified, it should be reported to authorities immediately and dealt with quickly, Chen said.

Animal epidemic protection work should also be strengthened, to reduce future deaths, he added.