Media playback is unsupported on your device Media caption The BBC's Martin Patience: “Local reports suggest that the animals were dumped by farms lying upstream”

Workers in China are continuing to collect dead pigs from a river near Shanghai, with more than 2,000 carcasses reportedly recovered so far.

Officials say they have to act quickly to remove the pigs, as the Huangpu River is a major source of drinking water for the city.

They are investigating the cause of the deaths and suspect the pigs were dumped by farms upriver.

Bloggers have criticised what some see as a slow government response.

Workers aboard boats are using long-handled rakes to pull out the bloated carcasses, which started appearing in the river on Thursday, according to reports.

Image caption The pigs have washed ashore along the river

"We have to act quickly to remove them all for fear of causing water pollution," Xu Rong, an environmental official, told state-run Global Times newspaper.

He added that the cause of the pigs' deaths may be determined in a few days.

It is still not clear why the animals were dumped in the river in the first place or who was behind it, says the BBC's Martin Patience in Beijing.

It is suspected that the pigs may have come from farms in neighbouring Zhejiang province, local reports say.

Officials say water supplies have not been affected so far and they are closely testing samples from the river, but the public remain wary.

"Is this water still drinkable after dead pigs were found floating in it?" 60-year-old Liu Wanqing was quoted by state-run China Daily newspaper as saying.

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

The incident has also generated much discussion online.

"Well, since there supposedly is no problem in drinking this water, please forward this message, if you agree, to ask Shanghai's party secretary, mayor and water authority leaders if they will be the first ones to drink this meat soup?" lawyer Gan Yuanchun said on his microblog.

Another blogger by the name of Ting Tao was quoted by Reuters news agency as saying: "Related government departments should seriously investigate this and get to the bottom of it... The government should really pay attention to people's lives."