Police on Friday morning detained a man suspected of using a knife to injure 22 students and a villager at the gate of a primary school in Central China's Henan province.

Min Yingjun, a 36-year-old villager, attacked students at Chenpeng Village Primary School in Guangshan county in the city of Xinyang at about 7:40 am, said Liu Qingdong, head of the county government's publicity department.

The injured students were sent to three hospitals in the county. Their injuries were not considered life-threatening.

The motive behind the attack remains unclear and the case is still under investigation.

Hearing of the violence, many Internet users went online to condemn it in micro blogs.

"It's raining in Guangshan now," wrote Li Kai, a reporter at the Dahe Daily. "It must be God weeping for innocent children. I can't understand why the suspect was so cold-blooded."

It wasn't the first time students in China had become the victims of such acts of violence.

Zheng Minsheng, a former community doctor, stabbed eight children to death and injured five others in front of a primary school in Nanping of South China's Fujian province on March 23, 2010.

Yang Jiaqin, a former village doctor with a mental illness, used a knife to kill an 8-year-old boy and an 80-year-old woman and injured three other children and two other adults in front of a primary school in Hepu county, the Guangxi Zhuang autonomous region, in April 2010.

Wang Yonglai, 45, a villager from Weifang in East China's Shandong province, broke into a local kindergarten and attacked children with a hammer in April 2010, injuring five. He then set himself on fire and died from his injuries.

Most of the culprits in these crimes have been middle-aged men who were dissatisfied with their lives and pessimistic about their futures, said Yang Yongchao, a psychologist at Zhengzhou No 8 People's Hospital.

Some of them had become resentful of society after their attempts to improve their livelihood were frustrated, Yang said.

Chen Wei, a Beijing-based lawyer with Yingke Law Firm who specializes in cases involving women and children, said certain Chinese schools, especially in rural and poor areas, have little or no security measures in place to protect students.

"Some schools have no gate watchmen or security guards, which has the potential to endanger students," she said. "And malicious adults at times will try to get a reaction by attacking children, who tend to be weak and can't really fight back."

If certain people have a conflict with a neighbor, they may try to get revenge by hurting the neighbor's child, she said.

Others, if they think they have been treated unfairly, will resort to extreme measures to attract attention to their cases, she added.

Chen suggested that it is safer for parents to escort their children inside schools rather than leaving them at the gate.