Officers from the northern Cao Bang Province joined in a raid of a rented house where the suspects lived on Thursday night and took in five women who had agreed to sell their babies including one who is eight months pregnant.

They said three other mothers had been taken to China to deliver their babies for sale.

The police described it as a large trafficking gang comprising Vietnamese and foreign members.

They have detained Mai Minh Chung, 36, and two other Vietnamese suspects. Investigation found Chung joined the operation in April 2019, using social networks to look for pregnant women who wished to sell their babies. For each successful transaction, the mother would receive VND80 million ($3,460) and Chung VND30 million.

The babies rescued Thursday have been handed to the Vietnam Women's Union’s Center for Women and Development and the police are continuing their investigation.

Vietnam is a human trafficking hotspot with the crime generating tens of billions of dollars annually, according to the Ministry of Public Security.

There have been over 3,400 victims of trafficking since 2013, over 90 percent of them women, children and people from ethnic minority communities.

Eighty percent of victims end up in China, which suffers from one of the worst gender imbalances due to its one-child policy and illegal abortion of female fetuses by parents who prefer sons, leading to increased trafficking of Vietnamese women and baby girls to that country.