Chinese health officials and police were Wednesday probing the mysterious deaths of hundreds of pigs and dogs whose carcasses were discovered in a central Chinese city, authorities said.

A total of 410 pigs and 122 dogs died Monday in a village within the city of Yanshi, according to a statement on the city's website. The deaths came after the discovery of more than 16,000 dead pigs last month in Shanghai's main river sparked public health concerns.

The statement said that livestock experts have eliminated an animal epidemic or the H7N9 strain of bird flu as the cause of the deaths of the pigs and dogs.

But all chemical plants in the area near to where the dead animals were found have been ordered to suspend operations, their power supplies have been cut off and managers are not allowed to leave as part of a police probe, the statement said.

The state-run Xinhua news agency reported that some village residents blamed the deaths on gas emissions from a local chemical plant, saying there had been an "extremely strong odour" on Monday morning.

The city of Yanshi, located in central China's Henan province, has a population of 558,800 people, according to Chinese government figures.

The deaths of the pigs found in Shanghai's Huangpu river, which supplies almost a quarter of the commercial city's drinking water, highlighted public health fears in China.

Authorities announced about two weeks ago that they had found the H7N9 strain of avian influenza in people for the first time. It has so far killed 16 people and infected 78, mostly in eastern China.

No vaccine to protect against the virus currently exists.

Health authorities in China say they do not know exactly how the virus is spreading, but it is believed to be crossing to humans from birds, triggering mass poultry culls in several cities.