Beijing (AFP) - A man who aided a senior citizen only to be accused of knocking him down has committed suicide in the face of demands for compensation, Chinese media reported Wednesday.

The story is an extreme case of a Good Samaritan tale gone sour in China, where recent reports of helpers facing huge financial demands have triggered a heated debate over the country's law and morals.

Wu Weiqing, 46, from Dongyuan in the southern province of Guangdong, was riding his motorbike on New Year's Eve when he came across an elderly man who appeared to have been knocked over, Wu's widow told the Southern Metropolis Daily newspaper.

Wu helped the man up and drove him to a local clinic, she said, where he paid 3,500 yuan ($580) in medical fees for him.

"My husband never imagined that the old man and his family would turn around and insist that he was the one who struck him down and demand that we pay hundreds of thousands of yuan in damages," Wu's widow said.

His daughter Wu Haiyan told the Guangzhou Daily newspaper that two days later her father told friends and relatives the old man's family was demanding a huge sum for "medical fees".

"My dad called me and said that he didn't want to die, that he was being hounded to death," she said.

"He felt vexed that he himself would be asked for money by the same old man he had helped, and he thought it better to die to prove his innocence rather than drag his family down."

He gave her instructions for his funeral, she said, and hours later his body was found in a pond.

The family of the old man, surnamed Zhou, denied to local media they had requested huge sums and maintained Wu had hit him.

"If he hadn't hit my father with the motorbike, why would he be so kind as to bring my dad to the hospital and pay for his medical expenses himself?" the old man's eldest daughter told the Guangzhou Daily.

Authorities have opened an investigation, the official Xinhua news agency said.

There have been several high-profile attempts by people claiming to have been injured to extort money from those who have helped them.

In one well-known 2009 case, a driver named Xu Yunhe came to the aid of an elderly woman in the northeast city of Tianjin. The woman later claimed that Xu had hit her, and a court ordered Xu to pay her 100,000 yuan ($16,500), on the grounds that he would not have helped if he was not responsible.

In another oft-cited case, in 2011 a toddler named Yue Yue in Guangdong province was run over by two separate vehicles and later died after being ignored by more than a dozen passers-by.

The public outrage over her death led the nearby city of Shenzhen to implement a "Good Samaritan" law two years later in a bid to encourage bystanders to help strangers in need.

Wu's case sparked renewed debate among Chinese social media users over whether the country is turning into a society of bystanders.

"If good people rescue the wounded only to meet this kind of end, how cold and indifferent will this society become?" one user wrote on Sina Weibo, China's equivalent of Twitter. "Farewell, Brother Wu."