The bloodiest known incident of unrest in China since the massacre that ended the Tiananmen Square protests in 1989 embarrassed China's president, Hu Jintao, into skipping the G8 summit in Italy. That is not surprising. Though distant from Beijing, the unrest in Xinjiang calls into question basic assumptions about China made by both the government and foreign investors: that Chinese citizens are ready to trade political dignity and fairness for economic progress and wealth; and that irrational forces, such as religion and ethnic nationalism, are distractions that can be bludgeoned away to enable the smooth technocratic transformation of society.

You're no Dalai Lama, Ms Kadeer

The Uighurs' plight is like that of the Tibetans: unfairness is not a side issue. Like the anti-Chinese riots last year in Lhasa, Tibet's capital, the savagery in Urumqi shows that modernisation does not always dampen resentment against Chinese rule. For both the Uighurs and the Tibetans, economic development has been inseparable from immigration by ethnic-Han Chinese, 92 per cent of China's population. But the two minorities present very different problems for the Beijing regime.

The Uighurs have never captured the West's attention in the way that Tibet has. While the saintly Dalai Lama has won the Nobel peace prize and become a friend to Hollywood stars, few outside the Islamic world have heard of Isa Yusuf Alptekin, exiled head of the Islamic Republic of East Turkestan, who died in 1995, aged 94, or of Rebiya Kadeer, a Uighur businesswoman who is the movement's new figurehead. The Chinese have also managed to persuade foreigners that the protests in Xinjiang are linked to jihadist terrorism: there are connections to the Taliban in Pakistan and Afghanistan, and almost two dozen Uighurs have spent time in Guantánamo Bay.

Although Tibet has garnered more headlines, the Uighurs probably represent a greater threat to the regime in Beijing. An uprising in western Xinjiang around Kashgar in 1990 was swiftly put down; pro-independence protests in 1997 led to bloodshed, and last year there were several terrorist attacks, including one in Kashgar in which 17 policemen died. The Uighurs' resentments also have the scope to inflame Muslim sentiment not just in China (which has more Muslims than Saudi Arabia) but throughout the Islamic world.

The rioters were obviously not terrorists, so China has tried to make a scapegoat out of Ms Kadeer this time. But the idea that this revolt was planned seems fanciful. The pent-up anger vented on the streets of Urumqi was chaotic, ignited by reports of the deaths of at least two Uighur toy-factory workers after they had been falsely accused of rape. The violence in Xinjiang was crude, racist stuff on both sides, with the Han Chinese suffering the brunt of it.

The fighting was nasty enough in itself, but its underlying causes should worry Beijing even more. Many Uighurs believe their land, traditions and religion are being swamped by decades of Han immigration, which has seen the proportion of Uighurs in Xinjiang shrink from about 75 per cent in 1949 to 45 per cent now. They are less likely to advance in the civil service, and many feel that Han Chinese do better in business too. They are fed up with their lot as despised, second-class citizens. Like Tibetans, Uighurs feel colonised, as Xinjiang's natural resources — it is rich in oil and gas — benefit the rich coastal regions. Meanwhile, for some Han Chinese, the Uighurs seem ungrateful and backward, pampered by the state with preferential policies, such as being allowed to have more children.

These prejudices are fed by another Chinese failing: the habit of secrecy and censorship. Lies and partial truths spread fast. Confronted with a choice of ugly rumours — as about the toy-factory case — many are inclined to believe the ugliest. At least China seems to have learnt from the riots in Lhasa last year: the ethnic-Tibetan violence against innocent Han Chinese got less coverage than China's repressive response. This time, China allowed foreign reporters into Urumqi.

That aside, China's response to the Uighur revolt has been pretty standard. It poured troops in, rounding up hundreds of people and putting them behind bars. If the past is any guide, many will be detained for months; some will be tried and sentenced to death. China will blame an evil minority at home and abroad. It will make no attempt to acknowledge-let alone redress-the grievances behind the outburst. Tibet and Xinjiang will be suppressed as if they were unruly colonies.

The perils of disharmony

But is this sustainable? Tibetans and Uighurs are only two of the groups which may not accept the growth-for-freedom trade-off that China's government offers. There are the unknown numbers of adherents to the Falun Gong movement; tens of millions of Christians who cannot follow their faith freely but already probably outnumber the 75m members of the Communist Party; farmers who have been victims of local-authority land-grabs; and many young who, unlike their parents, take economic prosperity for granted and are frustrated by the restrictions on their liberty.

By resorting to repression, Beijing can easily contain the disruption in Xinjiang. Despite its xenophobic propaganda, the integrity of the People's Republic's territory is not under threat. But something just as important is: the harmony which the government espouses as China's greatest national value, and without which the regime will find it harder to survive.

© The Economist Newspaper Limited 2009