A third of primary schoolchildren in China are suffering from psychological ill-health as a result of classroom stress and parental pressure, according to a study published on Tuesday.

The problem is so bad that urgent measures are needed, warns the study, led by British and Chinese researchers.

The investigation surveyed 2,191 pupils aged nine to 12 in nine schools in urban and rural Zhejiang, a relatively prosperous coastal province in eastern China.

Eighty-one percent of the youngsters said they worried "a lot" about exams, 63 percent feared being punished by their teacher, 44 percent had been physically bullied at least sometimes – with boys likelier to be victims than girls – and 73 percent had been physically punished by their parents.

Most of the children complained they struggled to cope with the amount of homework they were assigned.

Over one-third reported headaches or abdominal pains – psychosomatic symptoms of stress – at least once a week. The most stressed children reported incidence of aches or pains of four times a week.

The investigation, led by Therese Hesketh, a professor at University College London (UCL) Centre for International Health and Development, pointed the finger at extreme competitiveness in China's education system, from the onset of primary school.

"The competitive and punitive educational environment leads to high levels of stress and psychosomatic symptoms," the authors say.

"Measures to reduce unnecessary stress on children in schools should be introduced urgently."

The paper appears in Archives of Disease in Childhood, a peer-reviewed journal of the British Medical Association (BMA).

The "urban" setting for the study was Hangzhou, the provincial capital of Zhejiang, while the "rural" setting was a poor county in Quzhou prefecture, in the west of the province.

The study highlights some of the complexities that, it says, explain the demands for academic excellence and intolerance of failure.

One factor is the country's dramatic rise in prosperity, which has created "previously unheard-off possibilities for upward mobility" and in turn stoked pressures on children to do well at school.

Other reasons are China's one-child policy and the Confucian traditions of respect for parents and elders, filial piety, obedience and discipline.

"The aspirations of many parents, who had limited educational opportunities themselves are now invested in their only children," it says.

Previous studies on school-related stress and its impact on health are few and generally come from Scandinavia.

A 2008 assessment among 10- to 13-year-old in Sweden found that 21 percent of boys of 30 percent of girls experienced headache, and 17 percent of boys and 28 percent of girls experienced abdominal pain at least once per week.