BEIJING – Clashes with riot police broke out in southwestern China last week after thousands of protesters besieged a government office, a human rights centre and a witness said on Monday.

Friday's incident in Chongqing city's Youyang county was sparked when relatives of a school student who had been stabbed to death by a schoolmate claimed they were beaten by police as they protested in front of the school.

The angry crowd then moved to the township government office, holding a banner saying 'Murder in the School', a witness who was working at a hotel next to the office told Reuters.

'More and more people gathered around the county government, and the whole street was jammed for hours,' she said by telephone.

The Hong Kong-based Information Centre for Human Rights and Democracy said the number of protesters was as much as 10,000.

But the witness said she was not sure how many people were actually protesting, as many were simply onlookers who sympathised with the victim's family.

Some in the crowd recognised an occupant of a government car as the deputy head of the county, demanded that he get out of the vehicle and then smashed its windows, the witness said.

Dozens of police carrying riot shields were sent to the scene and had water-bottles thrown at them, she said.

The human rights centre said that up to 200 police were involved, about 10 people were injured and several were detained.

A Youyang township government official confirmed the death of the middle-school student, but declined to give more details.

The local police, reached by telephone, declined to comment.

A widening gap between rich and poor, corruption and official abuses of power have fuelled demonstrations and riots across the the country and are often sparked by seemingly minor issues.

Last month, hundreds of Chinese students clashed with police and overturned and burnt their car after street inspectors beat up a female student.