Beijing: Seven Chinese middle school students died and 12 more were injured on Friday when a man wielding a knife attacked them outside their school in northwestern China, the local government said.

The attack happened around 6:10 p.m. outside a school in the town of Mizhi in Shaanxi province, according to the local county’s Weibo social media account, reports the Washington Post.

A 28-year-old man surnamed Zhao has been taken into custody, local police said.

The injured students are receiving emergency treatment at a hospital.

The Mizhi county government said Zhao had studied at the school, where he had been bullied.

China has strict gun-control laws, but this has not prevented a series of puzzling attacks on schools in recent years by people with grievances against society or with mental health issues. In June, a 22-year-old school dropout detonated a bomb outside a kindergarten in the city of Xuzhou, in the eastern coastal province of Jiangsu, killing eight people, including himself.

Sociologists have blamed the attacks on the stresses caused by a society undergoing rapid change, with rising inequality and huge pressures on young people to compete and succeed. They have also cited a lack of support for the mentally ill and a dysfunctional legal system in which people who feel they’ve been treated unfairly or have suffered injustice have few avenues to seek redress.