Police in Hanoi on Friday said they have saved nine girls including seven below 16 years of age from Chinese brothels.
The youngest girl was less then 13 years old, the police said.
Some of the rescued girls were starved if they refused to work, they added, after completing a rescue effort that took more than 10 days.
The police also arrested 19 people for allegedly organizing the ring from Hai Phong city and the northern provinces of Nam Dinh and Lao Cai. The organizers were also young, some below 16 years old, they said.
The ring was discovered on June 19 when Nguyen Thi Thuy was caught in Hanoi as she took a 17-year-old girl from Nam Dinh to Lao Cai to be sold in China.
Investigators found that the ring has sold women and children in at least 11 instances, including seven last month. Each girl was sold for VND3-12 million (US$157-629).
The girls were coerced into signing papers that said they were working to pay off debts before being sold to brothels, investigators found.
In one case, Quach Ngoc Dung, 20, had last month helped Pham Thi Trang, 15, pay her Internet fees at a shop in Hai Phong, springing a debt trap.