Attackers have crashed two cars into shoppers at a market in the Xinjiang capital, Urumqi, and thrown explosives, killing 31 people, Chinese reports say.
One of the vehicles exploded in the attack, which happened on Thursday morning. More than 90 people were hurt, state-run Xinhua news agency said.
The Ministry of Public Security called it a "violent terrorist incident".
There are periodic outbreaks of violence in Xinjiang, which is home to the Muslim Uighur minority group.
Last month a bomb attack at a station in Urumqi killed three people and injured dozens more. China blamed the attack on Uighur separatists.