Thousands of villagers in Fujian clashed with riot police, smashed police vehicles and took government officials hostage in the latest peaceful mainland protest over industrial pollution to turn violent. Villagers and the authorities in the city of Quanzhou yesterday confirmed that more than 10,000 people had clashed with some 2,000 riot police on Monday night in the town of Fengwei. Police fired two warning shots and used tear gas to break up the crowd, witnesses said. The protesters pelted them with stones. The kidnapped officials were only rescued yesterday afternoon. At least a dozen people were wounded, including the deputy director of Fengwei and a police officer who are reportedly in critical condition. Authorities did not say how many villagers were hurt. The Quanzhou government accused 'a small group of people with ulterior motives' of instigating the protests, but did not elaborate. The source of the villagers' anger is a tannery and an oil refinery, discharges from which have poisoned their drinking water and caused cancer, they claim. They protested outside the sewage treatment plant because it handles their discharges. They began a peaceful protest two weeks ago. It swelled when the authorities ignored their complaints. Five days ago, protesters tried to sabotage the sewage plant and took two police officers hostage, the government said. They were later freed. On Monday, government officials accompanied by police tried to enter the plant, triggering the violent clashes, which lasted several hours. The Quanzhou government called the protesters 'rioters' and said its police chief, Communist Party boss Xu Gang and his deputy had gone to Fengwei. A joint venture between Sinopec, Exxon Mobil and Saudi Aramco - three of the world's biggest petrochemical companies - hopes to have a huge complex in Quanzhou ready by 2012. It will include an oil refinery and ethylene, polyethylene and polypropylene manufacturing plants. Fujian authorities say the project is part of its plan to make the city China's next big greenfield refinery site. Pollution has become a prime cause of social unrest and public discontent on the mainland, where years of breakneck economic growth, at the expense of the environment and public health, have left many areas heavily contaminated. The number of 'cancer villages', where the rate of cancers is much higher than the average, is growing rapidly. Yesterday villagers in Chengping, from where many of the protesters came, said many in their family, and neighbours, had died of stomach and oesophagal cancer in recent years, and blamed the discharge of untreated sewage. 'A foul smell from the sewage plant has permeated our village for years,' one villager said. (The plant opened in 2007.) 'In Fujian, one in three cancer patients comes from Quanzhou.' The villager would not give his name for fear of reprisals. Another villager whose mother has stomach cancer said: 'There are just too many cancer patients here.' Quanzhou authorities said the 50,000 tonnes of sewage the plant discharges each day met the strictest environmental standards. Oil refinery and chemical works have triggered huge protests in recent years. Guangdong recently relocated a controversial oil refinery from Nansha in Guangzhou, and a planned paraxylene factory in Xiamen, Fujian, was forced to relocate after more than 10,000 people marched against its construction.