The case of an 8-year-old Chinese girl who was reportedly abused by her foreign adoptive father has attracted widespread attention as she remains in critical condition on Thursday.

Phoebe, reportedly an orphaned girl who was beaten by a 50-year-old foreign man who adopted her, is currently being treated in the intensive care unit in a Beijing hospital after undergoing kidney surgery, The Legal Mirror reported on Thursday.

Doctors believe Phoebe's condition was caused by external force.

During two previous kidney operations, Phoebe claimed she was beaten by her adoptive father.

She is one of 11 children the man had adopted since 2004. Most of them suffered from congenital diseases. The man reportedly helped seek medication for them.

The jobless man claimed to have lived in China for 30 years and speaks fluent Chinese, The Legal Mirror quoted a foreign volunteer who goes by the pseudonym Xu Qiang, who has been in contact with the "family." However, his identity is unconfirmed.

According to Xu, the man hired a Chinese nanny who sometimes cooked for the children, but most of them are skinny and may have suffered from malnutrition.

The 11 kids never went to school. They have taken some US family education courses at home provided by the man and can speak English.

The man had publicly scolded or beaten the kids, Xu said, adding that the volunteers had reported these alleged incidents to the police.

"We usually see a nanny taking care of the children but we have not seen the foreign man. They moved out a few days ago," a staff member at the property management office in Shunyi district's Capital Paradise community where they previously lived, told the Global Times.

He disappeared after Pheobe was taken to the hospital and could not be reached.

Both the public security bureau in Shunyi district and the affiliated hospital of Capital Institute of Pediatrics where Phoebe is reportedly staying declined to comment on the case when reached by the Global Times.

Observers said the case reflects the absence of a monitoring system of children's rights which has made some orphans vulnerable to improper or unauthorized adoption.

"I believe it might be an unlawful adoption that the man had not gone through any legal procedure before he adopted the kids," Zhang Wenjuan, the former deputy director of Beijing Children's Legal Aid and Research Center, told the Global Times.

Foreigners need to apply to adoption agencies approved by both China and their home country if they want to adopt Chinese children, said Zhang.