The two traffickers were detected and stopped by police as they were boarding a flight from Ho Chi Minh City to Hanoi. They had three women with them, bought from their families for around US$470 (S$617) each, reports said of the October incident.
The women were to have been transported by road from Hanoi deep into southern China to marry the men who had bought them.
Trafficking of poor Vietnamese women to China is a thriving industry which China and Vietnam are struggling to contain.
Both countries hand down harsh punishments for trafficking. On Nov 28, a court in Vietnam gave six people involved in an earlier case similar to the October incident jail terms ranging from a suspended term to eight years. In China, the law punishes both buyers and traffickers in women and children. Traffickers can and do get five to 10 years in prison.
Yet the trafficking is on the rise.
In September, Ms Wang Ying, a deputy director at China's Ministry of Public Security, was quoted by the state-run China Daily as saying: "In recent days, some cross-border marriage brokerages and websites have published tempting advertisements offering Vietnamese brides for cross-border marriages, but most of these involve kidnappings."
The "marriage brokers" promised young women introductions to rich Chinese men from big cities, but many of the women were duped into being "sold" as brides to villagers in rural China, she said.
"Once their client takes a liking to a foreign girl, they cheat her and persuade her to have a wedding in Vietnam, then charge their male client 30,000 yuan (S$6,390) to 50,000 yuan as a service charge," said Ms Wang.
Nobody knows how many young women are sold across the border, either willingly - taking a chance with the people smugglers - or unwillingly, or simply duped. Activists involved in rescuing and rehabilitating young victims reckon the vast majority do not know what they are letting themselves in for.
But it is certain they are in the thousands every year.
Vietnam's big cities are humming, with the economy growing at well over 5 per cent so far this year. But in the countryside, grinding poverty remains. The poverty, combined with naivete, means a few hundred or a thousand US dollars are sometimes enough compensation for relatives to send a young woman to an unknown fate, at the hands of unknown men, in a foreign country. Sometimes the women go themselves, sold on promises made by brokers.
Some marriages turn out to be happy. In some cases, the men involved are also gullible and do not know they are party to trafficking.
But many of these arrangements entrap the women who find it difficult to leave. Some relationships can be abusive, with the women treated like slaves. Some women may even be sold again.
Too few of them manage to escape, perhaps finding a mobile phone and calling the police, or getting a friend to make a call, or borrowing money to pay off debts and buy their way back home.
Usually, most women are trafficked from northern Vietnam. From North Vietnam, it is easy to get a young woman across the border into China. Often, it is a matter of a short trek over mountains or just wading across a creek.
But because of high demand, traffickers are casting their net wider - to South Vietnam.
"Recently we have noticed more South Vietnamese going to China," says Ms Mimi Vu, Ho Chi Minh City-based director of advocacy and strategic partnerships at the Pacific Links Foundation.
The charity is active on the Vietnam-China border, running two shelters for rescued women and economically empowering poor young women by providing education and vocational training.
"Now we know that the demand for brides is so great that traffickers are willing to take the risk of transporting trafficking victims all the way to the north," Ms Vu said.
In one northern village, with a population of 337, about one-tenth had been trafficked to China in the past 18 months, she added.
"All of this is economically driven," she said. Young girls could fetch as much as US$1,600 to US$4,000 in China. Often, the local person who agrees to traffic them gets a cut of just US$100. The person may not be a close relative; they may just be facilitators. In many cases, families from hardscrabble or minority communities eking out a living in the mountains and possibly even illiterate just believe the women are going to a better life as the wife of a rich Chinese, and will send money back to them.
Vietnam is in Tier 2 of the US State Department's annual Trafficking in Persons (TIP) report, an influential assessment of the world's efforts in combating trafficking by country. By some estimates, globally as many as 27 million men, women and children are trafficking victims at any given time.
A Tier 2 listing means the country does not meet international norms in combating trafficking but is making the effort. Singapore is also in Tier 2 while Thailand and Malaysia are in Tier 3.
Vietnam's efforts have improved but remain under-resourced, a Western diplomat in Ho Chi Minh City said, asking not to be identified.
It is very difficult to educate rural people in remote areas, and to address their poverty, to stop young women from being sold, the diplomat said. Enforcement officers are also sometimes complicit, in return for a cut.
The Internet has extended the reach of the traffickers, noted the diplomat. International marriage brokers are illegal in Vietnam, but with the Internet they do not need a physical presence there.
"The government recognises the need to make more effort," the diplomat said. "The topic is discussed more now among officials, police and social workers. Efforts are broader and deeper now, including education, social work, reintegration and prosecution."
Mr Michael Brosowski, the Hanoi-based founder and chief executive of the Blue Dragon Children's Foundation, which works with Vietnamese children in crisis, believes law enforcers in Vietnam are doing a good job.
"It's an extremely difficult issue for them, it is international crime, it is Vietnamese people being taken to another country and being exploited, so it is very difficult to investigate or prosecute cases - but there's no doubt they are doing what they can."
Ultimately, the key to stopping trafficking is to ensure that the benefits of economic growth are spread to the poorest and most vulnerable of Vietnam's population. Until then, the women will always be at risk.
"The Chinese talk of buying Vietnamese brides like buying a car," said Ms Vu.
"What we have heard from some of our girls trafficked into China is they get a choice. Do you want to work in a brothel, or be a bride?"
China's gender imbalance fuelling demand
China's gender imbalance - the result of its once long-running one-child policy which triggered widespread sex-selective abortions in favour of male children - has fuelled a huge demand for women of marriage age or younger.
Exploitation and trafficking of young Vietnamese women for marriage is a trend of increasing concern, Vietnam's Ministry of Public Security said at a joint conference with the International Organisation for Migration (IOM) on July 30, with several government agencies and civil society groups present.
The conference took place at My Tho City, Tien Giang province - one of 18 provinces in South Vietnam considered hot spots for human trafficking - and was part of the government's 2011-2015 National Plan of Action against Human Trafficking.
The ministry reported that an average of 18,000 Vietnamese citizens - 92 per cent of them female - migrate to get married every year, with a significant number using illegal brokers.
From early 2008 to June this year, the authorities detected 1,100 cases of women trafficked for the purpose - or under the pretence - of marriage.
"The number of cases discovered by the police does not represent the extent of the problem," the conference agreed. "The line between the willing and the coerced is often blurred."
Separately, it has been reported that, in 2009, shelters across the country were providing relief services to over 12,000 trafficked women and children.
"Typically, women entering international marriages are from rural areas, unemployed and poorly educated," the IOM said in a report of the conference proceedings.
Women from Vietnam's south-west provinces account for most of foreign marriages. In the north, foreign marriages primarily take place in provinces bordering China.
The Department of Criminal Police reported that more than 60 per cent of human trafficking cases in southern Vietnam related to Taiwan and China. In the first six months of this year, there had been 310 cases of trafficking detected - a 60 per cent increase over the same period last year.
"Where previously illegal marriage brokerage was organised by individuals, now it is large organisations working across borders," the IOM said. "The legal framework remains loose and, as such, punishment is an administrative fine rather than a criminal sentence. Many cases cannot be brought to trial due to lack of evidence."
This article was first published on December 8, 2014. Get a copy of The Straits Times or go to straitstimes.com for more stories.