Photographs circulating on the internet of Thursday's riot at Shengda Economics, Trade and Management College showed smashed windows, damaged cars and a campus littered with debris and broken bicycles.

Hong Kong daily Ming Pao said up to 10,000 students took part in the riot.

Boycott

Students at the college, in Zhengzhou, Henan province, were said to be angry because of the college's decision to award them diplomas bearing its name.

They had believed that they would receive diplomas from the more prestigious Zhengzhou University, to which Shengda college is affiliated.

Higher education in China is expensive and many families go into debt to pay tuition fees. With competition for jobs intense, the quality of a degree can make all the difference.

One student, Xu, told the AFP news agency that there had been further violence over the weekend and thousands of students were still involved in a peaceful protest on campus.

"The stance of the school remains tough but if the institute does not resolve this issue, we will continue to boycott classes and examinations," Xu said.

Riot police have now confined the students to the campus, according to media reports.

The Chinese authorities are increasingly worried by incidents of social unrest, which they see as the biggest threat to their rule.

Endemic corruption and a growing divide between rich and poor have sparked an increase in public disturbances in recent years.

Student-led protests cause particular concern because students sparked the 1989 Tiananmen pro-democracy demonstrations which ended in a bloody crackdown.