Two underground abattoirs in eastern China are under investigation for pumping up to 120 litres of water over a 12-hour period into each cow to inflate their slaughter weight, state media reported today.

Images and videos taken by an undercover reporter at one of the slaughterhouses in Quanjiao, Anhui province shows water being pumped into cattle through tubes inserted into their nostrils before they were carved up and sold at a market in nearby Nanjing, a provincial state-controlled TV broadcaster reported.

Police in Nanjing have detained 29 suspects involved in the operations. The incidents have provoked outrage on social media over the cruelty inflicted on the animals as their ghastly ordeal emerged.

Images and videos taken by an undercover reporter at one of the abattoirs in Quanjiao, Anhui province shows water being pumped into cattle through tubes inserted into their nostrils

Workers whom the reporter spoke with said the process was cruel, though the foreman of the abattoir in Quanjiao, Anhui province said the process was 'painless'. 29 people were detained

Stills from the video released by Jiangsu Television showed a swollen cattle on its knees with tears in its eyes at the slaughterhouse in Quanjiao county. Another is seen collapsed on the ground.

Workers whom the reporter spoke with said the process was cruel, though the foreman of the abattoir said the process was 'painless'. The operation is repeated every day from 7pm till dawn.

'This is to make the cow heavier?' the reporter asked.

'Yes,' the employee said.

One of the cattle at the slaughterhouse was so swollen it collapsed onto the ground

Stills from the video clip released by Jiangsu Television showed a swollen cattle on its knees with tears in its eyes at the slaughterhouse in Quanjiao county

Water is pumped into the cattle before they are carved up and sold at a market in Nanjing

The case was reported to the Nanjing Municipal Public Security Bureau Food and Drug Environmental Crime Investigation Department, which immediately launched a snap investigation at both abattoirs.

When confronted by officers and reporters, a worker at an abattoir in Lai'an County said they were instructed by their employer to pump water into the cattle.

'He told us to remove the tubes if anyone knocks or tries to come in,' the worker admitted.

A number of social media users said the abattoir foreman should be pumped full of water instead.

A number of net users said the abattoir foreman should be pumped full of water instead

When confronted by officers and reporters, a worker at an abattoir in Lai'an County said they were instructed by their boss to pump water into the cattle

The case was reported to the Nanjing Municipal Public Security Bureau Food and Drug Environmental Crime Investigation Department, which immediately launched a snap investigation at both abattoirs, including one in Lai'an County (pictured)

'Cattle deserve to be treated with dignity too. Think about it, we should be grateful for their selflessness, which has helped fill our bellies,' one social media user wrote on Twitter-like Weibo.

Beef from the slaughterhouse had been popular due to its prices, which averaged 30 yuan (£3.38) a kg, about 10 per cent cheaper than its competitors, according to the broadcaster.

Consumption of beef in China is growing faster than for other meats. But with limited land to produce big herds to meet rising beef demand, China has been stepping up imports. Last year, China shipped in almost 700,000 tonnes of the red meat worth about £2.6 billion.