An 11-year-old mainland girl has been admitted to hospital with multiple injuries, revealing the first known case of child slavery in 50 years in Hong Kong.

Doctors said the case strongly resembled the long-outlawed practice of mui tsai (girl slave), in which rich Hong Kong families acquired child servants directly from impoverished parents or by kidnapping them.

The latest issue of the Hong Kong Medical Journal reported that the girl, from Guangdong, was bought for HK$1,000 by her father's sister.

She was put to work as a servant in her aunt's home from 5am to 10pm and was allegedly physically abused by the woman and her three children when she failed to meet their demands.

South China Morning Post