When a man with a cleaver walked into a kindergarten in China's Shaanxi province on Wednesday and hacked seven children and their teacher to death, shock was not the first public reaction.

After six such attacks in as many weeks, the mood among parents is approaching panic.

"We cannot feel safe any more. How come they can't stop this?" asked Li Wen, as she dropped off her daughter at a private Beijing kindergarten in a guarded compound in Beijing.

While killing sprees invariably prompt soul-searching, such attacks have rarely been made public in China and for many they are a vivid illustration of how the Chinese government is failing to live up to its pledge to create a "harmonious society".

Thirty years of breakneck growth without political reform have left millions of Chinese displaced, uprooted and confused. The killers' profiles mirror these social ills. Some were unemployed, others were involved in disputes over evictions and some had a history of mental illness.

"China's society is entering a high-risk phase. The unfair distribution of wealth, official corruption, the failure to safeguard people's basic needs, the inability to solve all these problems has created an inharmonious environment," says Yue Guo'an, a professor of social psychology at Nankai University in Tianjin.

Even Wen Jiabao, China's premier, acknowledged the deeper social implications of the attacks. "Apart from tight safety measures, we need to pay attention to addressing the root causes of these problems," Mr Wen said. "That includes dealing with social conflicts and dispute resolution at the grassroots level."

The first attack came on March 23, when a 42-year-old man killed eight children in a primary school in Fujian province with a knife. On the same day as his execution in late April, a similar attack occurred, followed by two more on consecutive days, one in a primary school and two in kindergartens. One of the attackers was unemployed and another had a history of mental illness.

Following the first attacks, the authorities beefed up security in schools and kindergartens.

The ministry of public security ordered local authorities to "screen residents for potential risks". The government banned reporting on the issue, citing a copycat effect.

"We are just a bunch of shameless spectators watching these murderers take the stage one after another," said a journalist in an online posting after being ordered to keep silent. "Sometimes, I am filled with despair for this country . . . there are still those who stubbornly repeat the mistakes of history - not letting people look, not letting people speak, not letting people think. Is this the way to establish peace on earth?"

Outside the silenced media, debate has been raging on what is wrong with China's society that would trigger such violence on society's most vulnerable.

Han Han, China's most popular blogger, said school killings had "become the most effective way of taking revenge on society", in a post that has since been taken down. "In a society without release valves, killing the weakest members has become a way of releasing [pressure]."

For those at risk of cracking, there is little help. A recent study co-financed by the World Health Organisation, found that 17.5 per cent of people in China have some kind of mental disorder, and 95 per cent of them have never seen a mental health professional.

"The combined category of neuropsychiatric conditions and suicide accounted for more than 20 per cent of the total burden of illness in China in 2004, making it the most important category of illness or injury," the study says. "But only 2.35 per cent of the government's health budget is spent on mental health and less than 15 per cent of the population had health insurance that covered psychiatric disorders."

"We need to strengthen psychological counselling throughout our society," says Luo Yuehong, head of the Xinyi Mental Rehabilitation Centre in Changsha. "People need to give more consideration to psychological problems."