Anger flared when Mr Li Guochao, 31, crashed into a lamppost after a local official threw a walkie-talkie at him as he sped away from a checkpoint, the city's public security bureau said in a statement.

Protests, led by Mr Li's angry family, broke into anti-police violence on Friday afternoon and lasted until the early hours of Saturday, with rioters burning a police car, the statement said.

The protest was the latest in a series of confrontations over social issues in China, where tens of thousands of riots erupt each year, many stemming from grievances over abuse of power, corruption or land grabs.

The street where the violence took place had returned to normal on Saturday afternoon, with vendors working and shops open, an AFP reporter at the scene said.

There was a beefed up police presence outside the station near where the riots took place.

'There were thousands of people trying to get close to the police station,' said one shop owner, who witnessed the riots.

'They tried to turn over the police car and people were smashing the windows with knives,' said the woman, who did not want to be named.

The police statement said the official who threw the walkie-talkie was not a police officer, and that the only police presence was a traffic officer 300 metres away from the checkpoint.

'However, the relatives of Mr Li Guochao thought that the checkpoint was organised by the police,' the statement said.

Mr Li had been stopped at the checkpoint in the city's Bao'an district, the statement said. He was carrying a passenger, who got off before Mr Li sped away.

An official tried to block his path, but was ignored and then threw the walkie-talkie at Mr Li. He lost control of his motorcycle and then crashed into the lamppost, the statement said.

He was taken to hospital where he died a few hours later, the statement said.

The relatives of Mr Li called together a group of around 30 people and at around 2.30pm, they carried Li's body to the police station, 'smashed things' and started setting off firecrackers, the statement said.

By 5.00 pm, more than 400 people had gathered at the police detachment with more than 2,000 others watching nearby. Some people threw stones and set fire to a police car, the statement said.

Police were only able to disperse the crowd at 2.00 am. There were no other reports of injuries.

The official who threw the walkie-talkie has been detained by police, the statement said.

Shenzhen is a thriving city of more than eight million people, lying just across the border from Hong Kong.

It has been transformed from a fishing village over the past 30 years after it was chosen by former Deng Xiaoping to be at the vanguard of economic reforms.

People living in the area told AFP the checkpoints had been set up to enforce a ban on motorcycles, set up after a spate of muggings by riders who snatched handbags.

One taxi driver in Shenzhen said it was widely believed that some of the police in the area were corrupt.

'The police say they are working for the people, but what actually happens is they just work for money,' said the driver, who only gave his surname as Mr Ma.

In June, tens of thousands of people rioted in southwest Guizhou province over claims police had covered up the alleged rape and murder of a teenage girl.

And last month a Shanghai court rejected an appeal from an unemployed man who became an unlikely cult hero after murdering six policemen in what he said was revenge for a wrongful arrest.

Mr Yang's case became a lightning rod for controversy by raising questions about police harassment, with some regarding him as a victim who stood up to abuse commonly suffered by marginalised people in Chinese society. -- AFP