Riots are reported to have taken place in a southern Chinese city in a protest over a land sale.Officials said rioters in Lufeng city in Guangdong province injured police officers and damaged government buildings during two days of unrest.There are tens of thousands of protests each year in China, some of which turn violent.Many are triggered by local grievances, such as farmers being kicked off their land to make way for development.One media report said several thousand people took part in the violence in Wukan village, which is part of Lufeng city.According to the South China Morning Post, protesters targeted a Communist Party building, a police station and an industrial park, amongst others.They believe that local party officials have sold their land to developers, the daily said.Images on internet forums showed villagers marching with a banner that read: \"Return my ancestral farmland\".Local officials said only a few hundred people had been involved.In a statement, they said that while a land deal had been the initial trigger, rumours that police had killed a child sparked further anger.\"On 22 September at around one in the afternoon, some villagers who had ulterior motives spread rumours about police killing a child, inciting some of the villagers to storm a border police station,\" the statement said.Local officials said 12 officers were hurt and six police cars burned. Residents said a number of protesters were also hurt, the South China Morning Post reported.Riots and protests like this are commonplace in China and there are hundreds every week, says the BBC\'s Michael Bristow in Beijing.Some are small in scale and centre on local grievances, but certain issues keep cropping upOne often-heard complaint is that corrupt officials collude with developers to sell off farmland without giving farmers the proper compensation.Laws are in place to protect farmers, but are often ignored at local level.Earlier this year, addressing the opening of the National People\'s Congress, Premier Wen Jiabao warned that if China wanted to ensure social stability it had to tackle corruption and address economic inequalities.