An extremely rare Amur leopard has been killed in China, state media reported Monday, as police searched for the suspected trapper.

The animal is listed as "critically endangered" on the International Union for the Conservation of Nature's Red List, one category below "extinct in the wild".

Global conservation organisation WWF on its website estimates the population in China at between just seven and 12, with another 20 to 25 in Russia.

The female leopard was found after two men were caught transporting its carcass out of a forest in China's northwestern Shaanxi province by van, the official Xinhua news agency reported.

Gao Jinlong, the wildlife protection chief in the city of Yanan, said the leopard was the first of its kind to be seen in the province in decades, Xinhua said.

"We've heard of rumours of a leopard here for many years, but never found any solid evidence," Gao said.

"It's such a great shame that the rumours were finally verified with the bloody truth," Gao said, according to Xinhua.

Police found the leopard's body and a steel wire trap inside the van, it added. One of the men -- the suspected trapper and killer of the animal -- fled the scene but the other was apprehended, the report said.

China placed the Amur leopard under "top grade national level protection" in 1983, according to Xinhua.

Earlier this month, police reportedly detained a man over the death of a rare Amur tiger discovered in the back of an SUV.

Pictures showing officers pulling the black-streaked tiger, wrapped in a plastic bag, out of a white vehicle went viral on China's Internet after they were posted online.

Trade in Amur tigers and leopards is outlawed under the Convention on International Trade in Endangered Species.

Conservationists cite increased logging as well as poaching of the animals for use in traditional Chinese medicine as among reasons for declining numbers of the species.