Huang Yanlai was 74 when he first raped 11-year-old Xiao Yu. He threatened her with a bamboo-harvesting knife while she was out gathering snails in the fields for her grandmother in Nan village, Guangxi province, in south-west China. Over the following two years, Xiao Yu (a nickname meaning Light Rain) was raped more than 50 times, her hands tied and a cloth stuffed in her mouth. She was a left-behind child, entrusted to relatives while her parents worked in distant cities. Her father returned home once a year. Told that his daughter was in trouble, he asked her what was wrong but she was too frightened to tell him. So he beat her up.

Xiao Yu’s story came to national attention after it was reported by state media. At the end of May it formed part of a study released by the Girls’ Protection Foundation, a charity in Beijing founded to increase awareness of child sexual abuse, a crime officials preferred not to discuss openly until recently. The study said that 968 cases of sexual abuse of children were reported in the media between 2013 and 2015, involving 1,790 victims. Wang Dawei of the People’s Public Security University says that for every case reported, at least seven are not. Because of the country’s size, however, the absolute numbers are staggering. Perhaps 25 million people under 18 are victims of abuse.

In any country, child sexual abuse is hard to measure. China has never conducted a nationwide survey, though it is talking about holding one in the next couple of years. And as there are no studies of abuse over time, it is hard to detect trends. Even so, there are reasons to believe that children are at growing risk.

First, China has huge numbers of “left-behind” children, like Xiao Yu. According to the All-China Women’s Federation, and Unicef, the UN agency for children, 61 million children below the age of 17 have been left in rural areas while one or both parents migrate for work. Over 30 million boys and girls, some as young as four, live in state boarding schools in villages, far from parents and often away from grandparents or guardians. Another 36 million children have migrated with their families to cities, but their parents are often too busy to look after them properly.

Another risk factor is a combination of ignorance, shame and legal uncertainty that makes it very difficult for children to defend themselves. Fei Yunxia works for the Girls’ Protection Foundation, the NGO that released the recent study of abuse cases. She travels to schools, giving sex-education classes. “No one tells these students about their bodies or how to protect themselves from harm,” she told Xinhua, a government news agency. Sex education in China is rare and never touches on abuse.

The lack of well-developed sex-crime laws means victims are often failed by the justice system. In Liaoning province eight school girls aged between 12 and 17 were kidnapped, stripped, beaten, and forced to watch and wait their turn while men who had paid $270 per visit raped them repeatedly in hotel rooms. The men were charged with having “sex with under-aged prostitutes”, a charge that shamed the victims into silence. The law that allowed child-rape victims to be classified as prostitutes was scrapped in 2015.

At the end of 2015 China adopted its first domestic-violence law. It says that preventing this is the “joint responsibility of the state, society and every family”. All this, says Ron Pouwels, Unicef’s head of child protection in China, means that “China gets it and is determined to do something about it.”