It said evidence from the scene of the attack late Saturday in Kunming by a group of knife-wielding people pointed to separatists from Xinjiang, a vast region home to the mostly-Muslim Uighur minority.
Victims described attackers dressed in black bursting into the station in the southwestern province of Yunnan and slashing indiscriminately.
The attack left at least 29 dead and more than 130 wounded, Xinhua said, citing local authorities.
Police shot dead at least four attackers, it said in an earlier report.
Xinjiang is periodically hit by violent clashes between locals and security forces but such attacks are rare elsewhere in China.
Beijing maintains that unrest in Xinjiang is caused by terrorist groups seeking an independent state, an account denied by Uighur rights groups who complain of widespread religious repression and economic discrimination.
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