NANNING - Authorities in south China's Guangxi Zhuang autonomous region are on the hunt for a cold-blooded menace currently at large on the Liujiang River.

However, the target of their manhunt is not a serial killer, but a group of piranha that recently attacked two people in the river.

Fishery authorities in the city of Liuzhou are offering 1,000 yuan ($157) to local residents for every confirmed piranha kill.

Two swimmers were attacked by at least three piranha in the Liujiang River over the weekend. One of the victims had parts of his finger bitten off by the fish.

Experts and fishery officials said the piranha may have been brought to the country from the Amazon region in South America. Guangxi's tropical climate makes it similar to the piranha's natural habitat.

"Piranha can reproduce very fast in environments similar to home. In addition, the piranha have no natural enemies here to keep their numbers in check," said Zhou Jie, an expert at the Fisheries Research Institute of Guangxi.

Liuzhou fishery authorities have invited experienced fishermen to hunt the fish, said Wei Yongwen, head of the city's fishery and animal husbandry bureau.

"We have also invited local fishermen to join us," said Yang Jun, another fishery official. "Fishing rods and bait are all being provided for fishermen to try their luck."

Several local residents were seen fishing on the river Tuesday night, using pork, mutton and liver to try and snag one of the fish and claim a reward.

Liuzhou's game fishing association has also urged its members to join the manhunt in order to "annihilate the man-eating fish in the shortest possible time."

The manhunt quickly spread to the Internet, with one Liuzhou-based blogger jokingly declaring "the people's war against the piranha has started!"

However, others remain skeptical of the government-led manhunt.

"Will other harmless fish in Liujiang fall victim to this campaign?" one blogger questioned. "What will the environmental impact be?"

Liu Haijun, a deputy head of Liuzhou's fishery supervision agency, said there have been no signs of the piranha, adding that five fishing boats have been looking for the fish since Monday.

"This means the number of piranha is likely rather small," Liu said."It is like looking for a needle in a haystack."

Zhou said he does not support a "blind manhunt," as it might threaten the ecological balance of the river. Other fish may be caught and killed as well, he said.