Piranhas - the voracious South American fish with a horrific reputation as man eaters -- are being blamed for attacking two residents in Liuzhou, South China's Guangxi Zhuang Autonomous Region, on Saturday, raising concerns over invasive alien species.

A Liuzhou resident, surnamed Zhang, claims to have been attacked by piranhas while bathing his pet dog along the city's Liujiang River. He said the fish bit into the palm of his hand and it only let go after he slammed the fish on the ground. He said he almost lost a chunk of flesh on his hand.

Zhang said he was shocked when he compared photos online with the attacking fish that he brought home.

He said his research showed he was bitten by a species of piranha native to the Amazon River and the Paraguay River in the Southern Hemisphere.

Zhang said the fish was still alive when it also bit his friend, surnamed Wu, who was teasing the fish.

"I assume these piranhas were dumped into the river by a tropical fish keeper, as this species can hardly survive naturally in the Liujiang River where water temperatures fall below what these fish require," Li Xinhui, a researcher at the Pearl River Fisheries Research Institute of the Chinese Academy of Fishery Sciences, told the Global Times.

"More follow-up investigation is needed to find out where on earth these tropical fishes came from, and whether they can survive," Li added.

Another expert on biodiversity from the Chinese Academy of Sciences told the Global Times that authorities need to better regulate the aquaculture market, through which most fish species invade the local environment.