By Jill McGivering
BBC News, Yunnan
As China opens up, people trafficking is emerging as a growing threat, but officials are reluctant to admit the scale of the problem.
Young girls in Yunnan want to go to cities or abroad to find jobs
In Yunnan province, young women are being sold as wives or to brothels and sweat shops in Thailand.
Life in the small Yunnan villages, close to the border with Burma, is very different from other parts of China where the economy is booming. This is a sleepy world of lush rice paddies, hillsides bursting with rubber trees and dotted with Buddhist temples.
Many villages here contain ethnic minorities whose language and culture has more in common with northern Thailand than with the Han Chinese.
Local people say trade across the border with Burma has fallen. So too has tourism. So for young people growing up in these small hillside villages, there is little opportunity.
Every year, thousands of them pack up and leave, heading for China's cities or crossing through Burma to Thailand in the hope of well-paid jobs.
Some do make money and come back to the villages to show off their success. That only encourages more young people to follow suit. But for an unknown but perhaps growing number, it all goes horribly wrong.
Trafficking is a hugely sensitive subject here. Officials do not really want to talk about it. And neither do victims. It took a lot of negotiating to find a young woman who was prepared to speak out for the first time and tell her story publicly.
Qing-qing is 19 now but when she was just seven years old, she and her mother were sold.
Qing-qing says human trafficking has become a cycle
"A woman my mother knows came to our house with some men we hadn't seen before," she told me. "My mother was tricked. They sold her as a bride to a man in eastern China."
The man beat her and her mother, she said, close to tears. At the age of 12, Qing-qing was forced to leave school and go to work. Their ordeal continued for eight years before they managed to escape and come home to their Yunnan village.
I asked her if this trafficking of vulnerable women still went on. "Yes," she said. "It's still going on in nearby villages."
"I know people who went through the same experience as my mother. Later some of them came back to the village to trick other people in the same way. It's become a cycle."
It was very difficult to find officials who could give a clear picture of the scale of trafficking.
One local Communist Party secretary told us it was certainly a potential threat, as more people migrated, but insisted it did not happen in his small community. But anecdotal evidence is widespread.
Long Hai-yu has been studying trafficking in Yunnan's villages for the last two years. She took me to one small village which she asked me not to name.
She talked to me about a case there involving two teenage girls who were recruited by strangers at the end of last year.
They were promised jobs in a shoe factory in Thailand, she said. But once the men took them across the border, they were blindfolded. The men started to threaten them and demand money from their families.
In fact, the two girls managed to raise the alarm and were rescued before they were taken any further, but Long Hai-yu said she thought they would have been sold into the Thai sex industry.
Not very much is known about who exactly the traffickers are. Long Hai-yu says they are Chinese people from another province, perhaps Sichuan province. They are not Thai, she explained, because it is too hard for Thai people to come to the villages to recruit girls.
As for numbers, it is impossible to know. Once young girls leave for another country like Thailand, it is hard for their families to find out what has happened to them.
Thousands cross from China into Burma every year
Long Hai-yu said that at just one nearby border point about 2,000 people cross into Burma every year.
"Many go to work in nightclubs and bars," she said, shrugging her shoulders. "Who knows how many are trafficked?"
'Can't happen here'
The Chinese authorities are just starting to take action. Here in Yunnan they have set up the country's first anti-trafficking programme.
I watched two young women act out a play, one playing a cruel trafficker and the other a desperate trafficking victim who despairs and finally kills herself. But not everyone in the audience got the message.
"Trafficking is when your boss doesn't give you all the money he owes you when you leave," said one girl.
A man sounded a reassuring note. "There's no need to worry," he said. "The government policy is good. Trafficking can't happen here."
But despite the reluctance to talk about it, all the evidence on the ground suggests trafficking is happening.
Researcher Long Hai-yu said she was extremely worried.
"The pattern is already changing," she told me. "Traffickers are targeting younger and younger girls, as young as 16."
As China opens up, its new freedoms are bringing new dangers. But they will be hard for the country's Communist system to address until it changes its culture of embarrassment and secrecy.