Authorities in China have detained five people as they investigate caches of 300 tonnes of dead pigs uncovered in southern mountains, state media said today, the latest in a string of scandals over the mishandling of sick livestock.

China is stepping up its fight on air, soil and water pollution with a new round of inspections to enforce tough new measures against anyone infringing environment protection laws.

The agricultural bureau ruled out foot-and-mouth disease and the H7 variant of avian flu, saying tests had found no threat of viruses spreading from the animals to humans

Environment officials in Huzhou city in Zhejiang province uncovered the carcasses, which had been dragged to the mountains and buried, instead of being burnt in line with the law on dead diseased livestock, the official Xinhua news agency said.

The company believed to be behind the latest scandal, the Huzhou Industrial and Medical Waste Treatment Co, buried the dead animals, which police estimate to have accumulated over four years, at three sites in the nearby Dayin mountains, Xinhua added.

A former manager of the company, Shi Zheng, now in jail for unrelated crimes, is suspected to be responsible for the decision to bury the pigs and five suspects have been detained, Xinhua cited Huzhou police as saying.

It was not possible to contact Shi for comment.

Telephone calls to a publicly-listed number for the waste treatment company went unanswered.

The agricultural bureau ruled out foot-and-mouth disease and the H7 variant of avian flu, saying tests had found no threat of viruses spreading from the animals to humans.

China, which is home to the world's largest swine flocks, as pork is its staple meat, has faced scandals over unexpected dead pigs before.

In 2013, 6,000 rotting pig carcasses floated down a river that supplies tap water to the commercial hub of Shanghai, drawing attention to a disease-riddled pig farm industry lacking in oversight.

Zhejiang authorities must "seek out and close loopholes in work to safely dispose of sick or dead livestock," China's agriculture ministry said on its website today, calling for a full investigation.

The pig remains had been an "open secret" for years and locals had long complained about a foul smell near the Dayin mountains, state media said.

But the source was only uncovered after an environmental inspector brought in diggers, following a complaint by a resident of the area.