A man wielding a knife climbed over the wall of a kindergarten in China and attacked 11 students, wounding them, according to Chinese state media.

According to Reuters, the 41-year-old man entered the school in the southern Guangxi Zhuang autonomous region mid-afternoon, claiming he was there to pick up his son.

The official Xinhua news agency quoted local police as saying that while three of the children sustained life-threatening injuries, all of the children were sent to hospital for treatment, according to local media. A suspect is currently in police custody but it is not yet known what the motive was for the attack. Police are currently investigating.

According to Fox News, while violent crime is rare in China, there has been a series of knife and axe attacks in recent years, many targeting children. The AP notes that tight controls mean that gun crimes are rare in China and make knives and sometimes explosives the weapons used in mass attacks in the country.

Last year, a man in the southern province of Hainan stabbed 10 children before killing himself, authorities said. In 2014, a group of knife-wielding men attacked a train station in southwestern China on Saturday, killing at least 29 people and injuring more than 130 others. Another man killed three students at a school in 2014 before jumping off a building.

In April 2010, a man stabbed 29 school children and three teachers at a nursery in Taixing city, Jiangsu province in Eastern China. Xu Yuyuan, 47, was sentenced to death for the attack, according to state media Xinjua at the time.

The AP notes that China has seen several other cases of disgruntled people with mental illness seeking out children in "revenge attacks": "Attackers often seek out the vulnerable, hoping to amplify their outrage before they themselves often commit suicide," explains the outlet. "News of one mass killing often serves as inspiration and blueprint to other potential mass killers"

"The social environment is a factor behind attacks in China," Ku Jianhui, a lawyer with the Beijing Xindong law firm, told the outlet. "A person who chooses extreme acts to voice his or her grievances usually believes that his or her cases were unable to be handled fairly through normal channels or legal procedures."

The Sun reports that China's Ministry of Education responded to those events by ordering schools to increase security and prevent strangers from going on campuses.