The report, by the London-based Korea Future Initiative (KFI), includes shocking first-hand reports of girls as young as 12 being raped and women being forced to participate in cybersex for days without eating, CNN reported on Tuesday.
The KFI's report took two years to compile, the group said. The authors said they interviewed more than 45 survivors and victims of sexual violence whose testimony pieced together a "complex and interconnected illicit industry that accrues vast profits from trafficked women and girls".
There were no official statistics on the number of North Koreans that leave the country and settle outside South Korea. Aid groups have reported that tens of thousands of North Koreans live in China as refugees, according to a 2014 UN report.
The KFI a non-profit that focuses on North Korean women, children and minorities who are the victims of human rights abuses in the report claimed that the number could be as high as 200,000.
It estimated that as many as 60 per cent of female North Korean refugees in China were trafficked into the sex trade.
"At a time when significant global capital is invested in China and, more recently, political capital expended on North Korea, it is a damning indictment that North Korean women and girls are left languishing in the sex trade," the organization said.
"Condemnation is insufficient. Only tangible acts can dismantle China's sex trade, confront a North Korean regime that abhors women, and rescue sex slaves scattered across brothels, remote townships, and cybersex dens in mainland China."
A 98-page report from Human Rights Watch published last November reached similar conclusions as the KFI regarding the risks female defectors face, CNN reported.
The US State Department also acknowledged reports of violence against women defectors in its 2018 report on human rights practices in North Korea.