GUANGZHOU - Police have detained a market trader over accusations that he beat his 2-year-old daughter so badly she was left with severe kidney damage.

The suspect, identified only as Zhang, was taken into custody along with his live-in girlfriend, a woman surnamed Liu.

Authorities acted after Yi Yi, the girl, was admitted to Guangzhou Zhujiang Hospital in Guangdong province, where doctors say she is in a critical condition.

"She has serious kidney damage," Tao Shaohua, a senior pediatrician, told Guangzhou Daily on Monday.

"However, her heart and liver functions have returned to normal."

Yi Yi, who was originally from Central China's Hunan province, was transferred to Guangzhou from a hospital in the nearby city of Zhuhai late last week. She was initially diagnosed with heart, kidney and liver problems, as well as several bone fractures.

A special team of senior medics has now been formed to take care of her, Tao said.

The girl's mother, named A Qin, who divorced Zhang about a year ago, is now at her daughter's bedside.

The case has outraged domestic abuse prevention campaigners, legal professionals and the public.

Zhuhai's public security bureau confirmed that Zhang, an aquatic products salesman at Zhuhai's Xiawan bazaar, and Liu are suspected of inflicting Yi Yi's injuries.

Both have denied the allegation, with Zhang claiming his daughter was hurt "in a fall", Guangzhou Daily reported.

As of Sunday, well-wishers had donated several thousand yuan to help Yi Yi's family pay for her medical bills, added the report.Statistics provided by the Guangdong Women's Federation showed that reported cases of domestic violence involving children have increased 20 percent year-on-year in the province during the past two decades, with many victims suffering serious injuries.

"There should be more NGOs working to fight domestic violence, particularly against children," Yang Shiqiang, director of federation's rights and interests department, was quoted as saying by Guangzhou Daily.

"These groups can join hands with women's federations to help children in need," she said.

Wen Lanzi, director of the federation, added: "The maltreatment of children should be condemned by society. Children should have happy childhoods under the protection of relevant departments and their parents."

Chen Xiaoda, a lawyer based in Guangzhou, told China Daily that, if Zhang and Liu are found guilty in a court of law, they should be "seriously punished ... to deter others and prevent similar cases".