HANZHONG, China – A man charged into a kindergarten in northwestern China with a cleaver Wednesday and hacked to death seven children and two adults — the fifth such rampage in less than two months. The attacker then went home and killed himself.

The assault, which left 11 other children hospitalized, occurred despite heightened security countrywide, with gates and cameras installed at some schools and additional police and guards posted at entrances.

It was not clear if security had been increased at the school on the outskirts of Hanzhong, a relatively poor area in the heart of China. Images taken from local TV and posted online showed the school, which only had about 20 students, in a tumble-down, two-story farmhouse.

Sociologists say the recent attacks that have left 17 dead and scores wounded reflect the tragic consequences of ignoring mental illness and rising stress resulting from huge social inequalities in China's fast-changing society.

"The perpetrators have contracted a 'social psychological infectious disease' that shows itself in a desire to take revenge on society," said Zhou Xiaozheng of Beijing's Renmin University.

"They pick children as targets because they are the weakest and most vulnerable," Zhou said.

Wednesday's carnage started as class was beginning at 8:20 a.m. at the private Shengshui Temple Kindergarten, the local government said.

The assailant, identified as 48-year-old Wu Huanming, entered the kindergarten and killed school administrator Wu Hongying and a student on the spot, then began hacking at the 18 others, according to the city government's statement.

Six students and Wu Hongying's 80-year-old mother died later in the hospital of their wounds, it said. None of the 11 hospitalized survivors was in immediate danger.

Wu is a common Chinese surname, and it wasn't clear if the assailant and administrator were related.

Citing the police, the official Xinhua News Agency said Wu Huanming had rented his house to Wu Hongying for the kindergarten without government approval. He then demanded the property back, but Wu Hongying had asked to hold onto it until the children went on summer vacation.

The ages of the children killed were not disclosed, but kindergarten students would typically be 5 or younger. Xinhua said they were five boys and two girls.

The recent attacks are classic "copycat crimes," the effects of which may be amplified by media coverage, Zhou said.

Boosting security at schools would provide only a temporary solution unless the root problems of social injustice and economic inequality are addressed, he said.

It's also difficult to protect so many places.

About 500 kindergartens, primary and high schools in Beijing have hired more than 2,000 professional security guards to increase safety, said He Gang, a police officer at the Beijing Public Security Bureau. Thousands more guards are needed for the city's remaining 4,500 kindergartens, primary and high schools, He said.

Early reports on Wednesday's attack were removed from Chinese websites or moved to less prominent pages. There was no mention of it on state television's national evening news report — which instead announced an urgent directive from the education and public security ministries to further protect schools.

State media have steered clear of examining what might be motivating school attackers, preferring to focus on security.

The government has sought to show it has the problem under control, mindful especially of worries among middle-class families who, limited in most cases to one child due to population control policies, invest huge amounts of money and effort to raise their offspring.

Recent scandals in which children have been the main victims have sparked public anger and occasional protests, such as when at least 3,000 children across China were found to have lead poisoning from polluting factories built too close to villages, and more than 300,000 infants were sickened by tainted baby milk powder.

The Hanzhong city government vowed to "leave no stone unturned, learn from the mistakes, and strictly ensure nothing happens like this again."

The city government said about 2,000 police officers and security guards had been assigned to patrol public schools, kindergartens and surrounding areas beginning last week. The city has a population of nearly 4 million.

Parents and grandparents waiting to pick up children at schools in Beijing and Shanghai said they were reassured by the increased security.

"When we hear about those attacks on children, all parents worry. We don't let the child walk home alone," said Guo Xiumei, 52, waiting to pick up her 7-year-old grandson at Beijing's Yonganli Elementary School. Two police officers and a pair of security guards flanked the downtown school's tall metal gate.

In Shanghai, a father waiting in his car outside the Aiguo Elementary School, where a single uniformed policeman stood watch at the gate, said he would adjust his work schedule to drop off and pick up his daughter.

"Who knows how those people think? They shouldn't take out their dissatisfaction with society on innocent children. It's not fair," said the man, who gave only his surname, Su.

The string of assaults began with an attack on a primary school in March in the city of Nanping, where eight children were slashed to death by a former doctor with a history of mental health problems.

The man convicted for that crime was executed April 28, the same day a 33-year-old former teacher broke into a primary school in the southern city of Leizhou and wounded 15 students and a teacher with a knife.

The following day, in the city of Taixing, a 47-year-old unemployed man with a knife wounded 29 kindergarten students — five seriously — plus two teachers and a security guard.

Hours later, a farmer hit five elementary students with a hammer in the eastern city of Weifang before burning himself to death.

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Associated Press writer Gillian Wong, Christopher Bodeen and researcher Xi Yue in Beijing and researcher Ji Chen in Shanghai contributed to this report.