Hundreds of students have rioted against the police in central China after a fellow student was beaten up by city inspectors, witnesses said.
Students from a number of universities in Zhengzhou, Henan province, burned cars in the four-hour rampage.
They came out onto the streets after inspectors were accused of assaulting a woman student who had set up a street stall, knocking out her front teeth.
A number of inspectors have been disciplined over the incident.
The unrest broke out on Wednesday, after the student was beaten up for apparently selling items on the street without a licence.
As many as 1,000 students from at least three universities took part in the protest, the Hong Kong-based Information Center for Human Rights said.
As well as clashing with police, the students overturned cars belonging to police and inspectors and burned at least one of the vehicles.
"I was also selling things on the street, and I could not take it any more, when I saw them beating up a girl, so I joined the riot by throwing a brick at the inspectors," one student was quoted by Reuters news agency as saying.
Another said: "I saw more than 10 people running after an inspector and trying to beat him, and some other people overturned a car and set fire to it."
Roads were blocked into the night, and by Thursday morning the city was reported to be quiet.
The Chinese Communist Party is very uneasy about this kind of large protest and is deeply wary of social unrest, the BBC's James Reynolds in Beijing says.
But the central government also wants to show that it is prepared to take action against heavy-handed local authorities.
Six inspectors were detained, two were sacked and four were given official warnings, the local Dahe newspaper reported.