A police officer enters a building Thursday where kindergartners were attacked by a man with a knife in Taixing, China. Today, a hammer-wielding man attacked another kindergarten class in Weifang in what was the third such assault in as many days.

BEIJING — A farmer attacked kindergarten students with a hammer, injuring five, before burning himself to death today in China's third such assault in as many days and prompting the government to demand stricter school security nationwide.

Wang Yonglai used a motorcycle to break down the gate of the Shangzhuang Primary School in the eastern city of Weifang and struck a teacher who tried to block him before hitting students with the hammer, the official Xinhua News Agency said.

Wang then grabbed two children before pouring gasoline over his body and setting fire to himself. Teachers were able to pull the children away to safety, but Wang died. None of the five injured students had life-threatening injuries, Xinhua said.

The attack was confirmed by an employee at the Weifang Public Security information office. But the motive for Wang's rampage was unclear. Xinhua described him only as a local farmer.

State media either ignored or played down the attack, perhaps to discourage copycat attacks as some experts have urged or to avoid overshadowing the opening of the World Expo in Shanghai, a pet project of the communist government.

Most of the recent school attacks have been blamed on people with personal grudges or mental illness — seen as a growing problem because of feelings of social injustice and alienation in the fast-changing country.

The government today issued an urgent directive to schools to tighten security nationwide. In the capital, the Beijing Education Commission ordered armed police units to patrol nursery, primary and secondary schools starting Tuesday, the first day back to school after the May Day holiday. The police will be on site when classes begin and end.

The hammer attack follows a rampage Thursday by a 47-year-old unemployed man armed with an eight-inch knife at a kindergarten. Some 29 students, ages 4 and 5, were wounded — five of them seriously — at the school in Taixing city in neighboring Jiangsu province.

And on Wednesday, a 33-year-old former teacher broke into a primary school in the city of Leizhou in southern Guangdong province and wounded 15 students and a teacher with a knife. The attacker had been on sick leave from another school since 2006 for mental health problems.

In all, there have been five such attacks on schools in just more than a month and many more in preceding months and years — although gun crime and other extreme violence in China is comparatively rare. Sociologists suspect the recent school rampages — usually by lone, male attackers — could be copycat actions.