Eleven underage girls, one aged just 13, have been rescued from a prostitution ring in Shanghai, police said yesterday.

All of the children were tricked into traveling to the city from their homes in southwest China's Sichuan Province and neighboring Chongqing City, they said.

The case came to light in October, when a woman surnamed Zhao contacted police in Hejiang County, Sichuan, to report her 13-year-old daughter, surnamed Ren, missing.

Zhao said the child had last been seen at a birthday party on October 5, the West China Metropolis Daily reported yesterday.

Soon after her disappearance, Zhao said she received a phone call from Ren saying she had been sold to a pimp in Shanghai, along with 10 other teenage girls. But the call was quickly cut off and the mother was unable to find out any more details, the report said.

In the following weeks, police received a tipoff about other girls going missing, one of whom had left a note saying she had gone to Shanghai in search of work with a friend.

In the course of their investigation, Hejiang police apprehended a man seen with two young girls at the long-distance bus station in Hejiang.

When questioned, the suspect, who was not named, said he was taking the girls to his boss in Shanghai, who ran a prostitution ring, police said.

The alleged ringleader was identified as He Chunbiao, a 40-year-old native of Chongqing.

Meanwhile, Ren managed to send a text message to her mother from the cellphone of one of her "clients," telling her where she was being held.

She also said He's wife, Chen Yumei, had taken the girls' phones, was keeping them prisoners and had threatened to beat them.

Based on that information, police were able to track down the suspects and free the girls, all of whom were aged between 13 and 17.

Suspected ringleader He is accused of recruiting men to identify vulnerable girls and coax them into moving to Shanghai. Once in the city, He is alleged to have raped the girls and then forced them to work as prostitutes.

Eight people have been detained in connection with the alleged crimes.