Over 10 knife-wielding assailants stormed through a railway station in south-west China on Saturday, killing 29 and injuring 143, in what officials said was a terrorist attack by ethnic separatists from the far west of the country.

Four of the group were shot dead by police and a fifth was captured after the group stabbed and slashed people at random late on Saturday at the Kunming train station in Yunnan province. The remainder are being searched for.

The Chinese President Xi Jinping promised a harsh response to the attack, saying “all-out efforts” are being exerted to “severely punish in accordance with the law the violent terrorists and resolutely crack down on those who have been swollen with arrogance.”

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The country’s top police official Meng Jianzhu arrived in the city early on Sunday and officers have been rounding up members of the city's small Uighur community, believed to number no more than several dozen, for questioning about the attack and assailants.

Shape Created with Sketch. Chinese 'terror attack' in Kunming Show all 8 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. Chinese 'terror attack' in Kunming 1/8 China mass stabbing Chinese mourners light candles for the dead and injured at the scene of the terror attack at the railway station in Kunming Getty Images 2/8 China mass stabbing People outside the station where the attack took place 3/8 China mass stabbing Police investigate after a group of knife-wielding men attacked people at a train station in Kunming in south-west China Reuters 4/8 China mass stabbing Chinese police investigators inspect the scene of an attack at the railway station 5/8 China mass stabbing The ticket office after a group of armed men attacked people at Kunming railway station Reuters 6/8 China mass stabbing A Chinese police investigator inspects the scene 7/8 China mass stabbing Poilce patrol the area 8/8 China mass stabbing Emergency vehicles have flooded into the area 1/8 China mass stabbing Chinese mourners light candles for the dead and injured at the scene of the terror attack at the railway station in Kunming Getty Images 2/8 China mass stabbing People outside the station where the attack took place 3/8 China mass stabbing Police investigate after a group of knife-wielding men attacked people at a train station in Kunming in south-west China Reuters 4/8 China mass stabbing Chinese police investigators inspect the scene of an attack at the railway station 5/8 China mass stabbing The ticket office after a group of armed men attacked people at Kunming railway station Reuters 6/8 China mass stabbing A Chinese police investigator inspects the scene 7/8 China mass stabbing Poilce patrol the area 8/8 China mass stabbing Emergency vehicles have flooded into the area

Eyewitnesses said the attackers were dressed all in black and were wielding long knives. State broadcaster CCTV said at least two of the attackers were women - one of the dead and the captured one, who was later taken to a hospital for treatment.

The attackers' identities have not been confirmed, but the municipal government said evidence at the scene showed that it was “ a terrorist attack carried out by Xinjiang separatist forces,” according to the official Xinhua News Agency.

Graphic photographs surfacing on Sina Weibo, the Chinese equivalent of Twitter, showed a row of bloody bodies on the station concourse and at the Kunming No 1 hospital.

Qiao Yunao, a 16-year-old student, was waiting for a train at the station when the attack happened. He said he saw people crying out and running, and then a man cut another man's neck, drawing blood.

“I was freaking out, and ran to a fast food store, and many people were running in there to take refuge,” she told The Associated Press via Sina Weibo. “I saw two attackers, both men, one with a watermelon knife and the other with a fruit knife. They were running and chopping whoever they could.”

The Security Management Bureau, under the Ministry of Public Security, said the attack was a “severe violent crime” in its own message on Sina Weibo, adding: “No matter what motives the murderers hold, the killing of innocent people is against kindness and justice. The police will crack down the crimes in accordance with the law without any tolerance.”

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There is a simmering rebellion against Chinese rule by some members of the Muslim Uighur population in Xinjiang province, located in the extreme west of China where the country borders central Asia. The government has responded with heavy-handed security.

Clashes between Uighurs and members of China's ethnic Han majority are frequent in Xinjiang, Saturday's attack however happened more than 620 miles to the southeast in Yunnan, which has not had a history of such unrest.

The assault was the deadliest incident attributed to Uighur-Han conflict since 2009, when a Uighur mob first attacked and killed Han people, included women and children, at random on the streets of Urumqi, the capital of Xinjiang. A few days later, Han vigilante mobs attacked Uighurs in the same city. In total, nearly 200 people died.