“THIS should not be. It just should not be. I don’t understand.” Uttering these words as he tried to hold back tears, a retired train driver stood before a makeshift shrine in front of Kunming railway station, where on the evening of March 1st a group of assailants, clad in black and wielding long knives and cleavers, unleashed terrible carnage.

They stabbed and slashed indiscriminately, witnesses say, and sent people running frantically from the mayhem. It was over in a matter of minutes, but not soon enough. At least 29 people died and 140 were injured in the attack, which state media have called “China’s September 11th”. Authorities say it was an act of terrorism carried out by “Xinjiang extremists”, by implication ethnic Uighurs, a Muslim minority group from the north-west.

According to police, four attackers were killed on the spot and one—a woman, who was injured—was captured. Two days later police said that three more had been detained, and that the search for the perpetrators was over.

Except for the gun-toting police and the presence of the shrine—where people come to bow and offer flowers and fruit to honour the victims—the station has returned almost to normal, as the bustling hub of a second-tier city of 6m people. But the impact of the attack, on Kunming and on China, may be far-reaching. It could mark a disturbing escalation of China’s long-festering problem of ethnic tension.

Violence has occurred sporadically for years in Xinjiang, where most of China’s 10m Uighurs live and bristle under heavy-handed rule from Beijing. Uighurs are more like Central Asians in their culture and religion than like Chinese.

Most just about rub along with their Han Chinese neighbours, who now make up 40% of Xinjiang’s population. But discontent occasionally surfaces in the form of attacks with low-grade explosive devices and knives. In July 2009 nearly 200 people died in inter-ethnic riots in Urumqi, Xinjiang’s regional capital. In recent months, the number of attacks against security personnel has increased amid a broader official crackdown on religious and cultural practices, which China’s leaders worry fuel Uighur separatism. Only recently has violence looked like spreading to other parts of the country. In October five people died and dozens were injured in Tiananmen Square in Beijing, when a sport-utility vehicle crashed into pedestrians in front of the iconic portrait of Mao Zedong. Authorities also called that a terrorist attack and blamed it on a group, about which little is known, called the East Turkestan Islamic Movement. (East Turkestan was the name of a short-lived independent state in the region in the 1940s and is the name many Uighurs prefer over Xinjiang, the Chinese name.) No group claimed responsibility for the Tiananmen crash, nor has anyone done so for the Kunming massacre. Apart from eyewitnesses describing what they saw, there has been no independent way to confirm the details given by the authorities, including claims that black flags adorned with crescent moons and other evidence associated with “East Turkestan terror forces” were found at the scene. The bloodletting comes as a particular shock for Kunming. The city is the capital of Yunnan, which, despite being one of China’s most ethnically diverse provinces, has a reputation for tolerance and has suffered little of the turmoil familiar to Xinjiang or Tibet, another of China’s ethnic hotspots.

In Kunming’s main Uighur enclave, a district called Dashuying, residents say the attack does not bode well for their future. “The Chinese have always looked down on us, but it was bearable,” says Abdurkhman Khadar, a native of the Xinjiang city of Kashgar and owner of a Kunming flatbread bakery. Now, although nobody seems to think the killers came from his district, “the attitude of Han people has suddenly got even worse”. Stacks of flatbreads are piled in his shop. Since the attack his Han customers have stayed away. The police presence in Dashuying has also increased. Large vans guard intersections near the district, and police in full riot gear patrol the narrow alleys.

Most Han Chinese have reacted with bewildered horror. Always told that minorities receive preferential treatment in education and family planning, and with nothing ever reported in the Chinese press about the suppression of minority culture and religion, many Han are left wondering why the Uighurs are so angry. Some, along with the government, also feel annoyed at the perceived reluctance of foreign media and governments to call the attack terrorism. An American official finally said on March 3rd that, based on information in the Chinese media, “it appears to be an act of terrorism”.