The police searched houses on February 25 to investigate traders hired to take care of the newborn babies before selling them on to China.
Four mothers were arrested on suspicion of getting involved in the trafficking ring, while four babies were also rescued.
During the operation, the police also discovered an eight-month pregnant woman who had intended to sell her child once the baby is born, along with two other pregnant mothers who had been brought to China.
The police said the large-scale nature of the newborn trafficking ring involves the participation of both domestic and foreign suspects.
At present, the four babies are now being taken care of by a social welfare centre operated by the Vietnam Women’s Union.
The police are expanding the scope of investigation.