At least 31 people have died in an explosion in the capital of China's western region of Xinjiang.
More than 90 people were injured in the blast.
China's Ministry of Public Security described the explosion as a "serious violent terrorist incident".
State media reported that two vehicles rammed into a crowd of people at a morning market in the city of Urumqi.
Explosives were hurled from the vehicles, and one of the vehicles exploded.
Domestic security chief Meng Jianzhu vowed to "destroy the arrogance of violent terrorists", the statement said.
Public Security authorities have taken emergency measures, the statement added.
The blast comes at a time of heightened tension in the region.
China has blamed a string of violent attacks in recent months on separatist militants from Xinjiang, the traditional home of ethnic Muslim Uighurs.
One witness said he saw the aftermath of the blasts on his way to work.
"The air was full of the smell of gunpowder and the sound of sobbing," he said. "There were simply too many [casualties], old folks who were at the morning market."
In a posting on its Chinese-language microblog account, the US Embassy said it offered condolences to victims of the "violent attack", but stopped short of labelling it terrorism.
The Xinjiang government could not be immediately reached for comment.