Police in Central China's Hunan Province have rescued 40 women trafficked from Vietnam, and busted a human trafficking ring after a joint investigation. Thirty suspects have been arrested.

The Vietnamese women were trafficked to China for forced marriages. China suffers from one of the worst gender imbalances in the world, as families have historically preferred male children. As a result, millions of men cannot find Chinese brides – a key driver of trafficking.

Chinese traffickers have long collaborated with Vietnamese associates in the trade, local police said.

The suspects fall into four categories. First, Vietnamese traffickers. They usually look for rural women in their 20s or 30s, abduct them, drug them, or lure them to China with promises of good jobs or tourist trips. Second, the Chinese traffickers. The women are handed over to them upon arrival in China. They provide accommodation, contact agents, and transport the women across the country. Third, the middlemen, or matchmakers. Last but not least, the buyers.

In 2016, Vietnam reported 383 cases of human trafficking. There were 1,128 victims, up nearly 13 percent from the previous year. Most of the victims were uneducated women and children from poor areas.

China and Vietnam are tightening border management and expanding intelligence sharing in the fight against rampant cross-border trafficking of women.