Nguyen Thi Bien, 51, born into a poor family and not finishing elementary school, started working at a young age as a farmer and sometimes a baby sitter in her hometown in Hiep Hoa District, Bac Giang Province.

Speaking to the media after returning to Vietnam earlier this month, she said in 1991 she had befriended a man she remembers only as Quang.

He said he would help her go to China where she could easily find jobs, and she agreed.

She left with him for China without informing her family.

After they crossed the border, Quang sold her to a Chinese man and disappeared. She was taken to a house in a remote area and treated like a prisoner.

Without any knowledge about China or its language, she could not think of how to get out or escape back to Vietnam.

After being locked inside the house for a while, she was made to work and spent most of the time on farms.

Except to work or eat, she was never let out of the house.

"I cried all day, and every time I showed signs of wanting to get out, they [the man and his family] would threaten to beat me. I was so scared and had to do whatever they told me to do," she told Vietnam Plus.

In 28 years in China the only times she was allowed to leave the house was to go to the market.

Gradually she forgot how to write Vietnamese.

More than once the family promised to send her home one day if she kept working, but that day never came. For many years she believed she would die in China.

Around six months ago the police raided local households and found her without any ID.

They detained her for two weeks to investigate before bringing her to the border along Vietnam’s Lang Son Province and send her home.

Along with her were seven other northern Vietnamese who had also been tricked and sold in China.

Together they walked around 10 kilometers through a forest into Lang Son's capital town before splitting up.

In Lang Son, by chance she met Tran Van Huynh, a trader from her native Hiep Hoa District, who was there for business. Learning about her situation, Huynh posted her photos and information on social media along with the names of her parents and address in Vietnam.

The information finally reached Bien’s family.

On August 2 Huynh took her back to Bac Giang with him where she reunited with her family.

It is not known if she had children in China.

Her father, Nguyen Van Nhom, 82, said the family had presumed she had been sold in China and tried in vain to find her for many years.

Nguyen Thi Phuong, her sister, told the media that Bien has become much quieter and only speaks when asked something, and her Vietnamese is no longer very clear.

Tran Van Son, deputy head of Dong Lo Commune in Hiep Hoa District, said Bien had been a resident of the commune and missing since 1991.

The police are working on issuing her a new ID, he added.

China is the main destination for human trafficking victims from Vietnam.

In 80 percent of the 1,000 cases uncovered since 2016, the victims had been trafficked to China, the Ministry of Public Security said this month.

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

Besides the financial situation of victims, negligence, easy immigration procedures and gender imbalance in destination countries are the main reasons for human trafficking, according to police officers.

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.