Chinese officials have blamed separatists from the north-western Xinjiang region for a mass knife attack at a railway station that left 29 people dead and at least 130 wounded.
A group of attackers, dressed in black, burst into the station in the south-west city of Kunming and began stabbing people at random.
Images from the scene posted online showed bodies lying in pools of blood.
State news agency Xinhua said police shot at least four suspects dead.
A female suspect was arrested and is being treated in hospital for unspecified injuries while a search continues for others who fled the scene, the BBC's Celia Hatton in Beijing reports.
Authorities described the incident as an "organised, premeditated, violent terrorist attack".
The Kunming city government later said that evidence from the scene pointed to separatists from Xinjiang as being behind the attack.
It gave no details and the claim could not be verified.
Some of Xinjiang's minority Uighur Muslims want autonomy from Chinese rule and an end to state suppression of their religion.
Witnesses in Kunming said those who couldn't run quickly were cut down by the attackers' knives.
A survivor named Yang Haifei, who was wounded in the back and chest, told Xinhua he had been buying a train ticket when the attackers rushed into the station.
"I saw a person come straight at me with a long knife and I ran away with everyone," he said.
First reports said the attackers were only men, but witnesses and police later said the group also included women.
Chinese President Xi Jinping and Premier Li Keqiang sent condolences to the victims and their families.
President Xi urged "all-out efforts" to investigate the attack.
"Severely punish in accordance with the law the violent terrorists and resolutely crack down on those who have been swollen with arrogance," Xinhua quoted the president as saying.
The incident comes a few days before the opening of China's annual parliamentary session, the National People's Congress.
Our correspondent says domestic security is expected to top the agenda.
Last October China blamed Xinjiang separatists when a car was driven into a crowd of people on the edge of Beijing's Tiananamen Square, leaving five dead.