At least 27 people died in a knife attack at a train station in Kunming, south-west China, the state news agency Xinhua says.
Nothing is known so far about the motivation behind the attack, in which 109 people are said to have been hurt.
Xinhua gave few further details, and the men responsible have not been identified.
A local television station said several of the attackers had been shot by police, according to Associated Press.
Chinese state television described the incident as a “violent terror attack”.
Eyewitnesses said that the men started attacking people at random.
Social media users in China have been posting pictures of the attack on the internet, but correspondents say they are being taken down.
Mass stabbings are not uncommon in China, but none have been recently reported on this scale.
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