Blue Dragon, a non-profit organisation based in Hanoi, Vietnam knows that rescuing trafficking victims is anything but easy. Rescuers, who remain anonymous for their own safety, say they are often confronted by angry husbands, pimps and traffickers, AFP reported.

Tens of thousands of girls from poor countries such as Cambodia, Myanmar and Vietnam are trafficked into China, where an overwhelming surplus of marriage-age males has created a high demand for sex workers and even brides.

In some cases, the women are tricked with promises of well-paid jobs, while others are kidnapped and smuggled across borders.

Rescuers have received distress calls from everywhere, including phone calls and text messages from apps such as WeChat and QQ—the two most prominent messaging services in China.

At times, desperate victims do whatever it takes to escape. One case saw a woman fake an illness and check in at a hospital, where she called Blue Dragon for help. Her tip-off led rescuers to a remote location where she was sold off as a bride.

Rescue missions can take months to plan and execute given the high degree of risk involved. Up to eight victims per month are returned home by Blue Dragon, who receive one to two distress calls a day. Since 2007, Blue Dragon has assisted in rescuing around 400 women who were trafficked into China.