A teacher in Henan province has been detained over allegations that he has been molesting female students since early 2012.

Yang Shifu, born in 1958, worked at a primary school in Douchengou, a village in Nanyang.

Families went to police with allegations on Thursday, and Yang was detained that day, the Tongbai county government said in a statement on Monday.

According to authorities, Yang is suspected assaulting the students during class breaks when he would meet them to go over their homework.

The school principal was dismissed shortly after police received the report, and another man, Xu Haitao, was named temporary principal.

When the case came to light, the remote school had 68 students, 37 of them girls, in four grades and five teachers, including the dismissed principal, Xu said on Monday.

"Yang has only four years left until retirement," Xu said.

Yang, a native of the area, had been working at the school for more than 30 years.

Police are investigating the allegations but have declined to comment on the investigation. The school reopened on Monday, and classes resumed as usual.

Families said a male student had told them he had seen the teacher molest two girls in a classroom on May 21, Henan Business Daily reported.

After telling police, the families of 16 girls took them to a Tongbai hospital on Thursday for medical evaluations.

Dahe Daily reported that these evaluations revealed that nine of the 16 girls had broken hymens and others had some sort of injury.

The county government did not confirm those results on Monday and they said many of the students were "left-behind children", the children of migrant workers. Six of the children were left behind by both parents, and the others were left behind by one parent while the other resided at home.

In recent years, China has seen a rise in sexual assault cases among left-behind children who live alone or with their grandparents.

Research by Mirror Evening Daily and Beijing Children's Legal Aid and Research Center found that in a sample of 40 cases in recent years, nearly 40 percent of sexual assaults have occurred among left-behind children.

Due to limited communication and supervision, children of migrant families are more vulnerable, the report said.

"A rise of cases among migrant children also shows a lack of supervision from schools and education authorities," said Wang Peng, a lawyer at Han Wei Law Firm in Beijing.