Luong Thi Khay, 33, has been released on bail because she is pregnant while Lo Thi Thanh, 32, is in custody, police said Saturday.

According to the police, the two girls, whose identities they did not disclose, then aged 15 and 14, had sought Thanh’s help to go to China and find jobs there.

They are natives of Nga My, a remote commune in Tuong Duong District of Nghe An.

Thanh got in touch with Khay, and the two women contacted a Vietnamese woman living in China to sell the girls to Chinese men.

In July 2012 the girls were taken to China and sold for around 55,000 yuan ($8,600 then) each.

In April 2017, during a raid, Chinese police found one of the girls and sent her back to Vietnam.

But the girl, who is illiterate and without any support from her family or local officials, did not complain about Thanh and Khay.

In June this year the Nghe An criminal police collaborated with Blue Dragon, a Hanoi-based non-profit organization that has helped bring home 400 trafficked women and girls from China since 2007, to rescue the other girl and bring her back to Vietnam.

The second girl filed a complaint leading the police to arrest Thanh and Khay.

One of girls spent five years as the "wife" of a Chinese man and the other, seven years.

Both were beaten by either the men or their families and kept under constant watch. They managed to escape more than once but were caught each time.

Neither bore children.

China has been a top destination for human trafficking victims from Vietnam.

In 80 percent of the 1,000 trafficking cases uncovered since 2016, the victims were sold to China, the Ministry of Public Security said early this month.

Most victims were from northern border provinces and women or children.

Besides the financial situation of victims, police officers have said negligence, easy immigration procedures and gender imbalance in destination countries are also responsible for human trafficking.

China, the world’s most populous country, suffers from one of the worst gender imbalance rates due to its one-child policy and illicit abortion of female fetuses by parents wanting sons. This has led to increasing trafficking of Vietnamese women and girls.