* Anti-China protests turn angry, factories targeted
* Extent of damage unknown
* China's embassy warns businesses, citizens
HANOI, May 14 (Reuters) - Rioting broke out at industrial zones in southern Vietnam during protests by thousands of workers angered by Chinese oil drilling in a contested area of the South China Sea, officials said on Wednesday.
Workers smashed gates in the rioting on Tuesday and entered industrial parks housing factories in Binh Duong and Dong Nai provinces, which are central to Vietnam's sizable manufacturing interests.
The destruction comes amid high tensions between China and Vietnam, which have close trade and political ties despite a history of incursions and territorial battles that are the source of deep resentment among Vietnamese.
Vietnam's state-run newspapers and its television channels reported the rioting on Wednesday, but did not show photographs or any video footage.
"About 19,000 workers were demonstrating against China's violation of Vietnam's territorial waters," Tran Van Nam, vice chairman of Binh Duong people committee, told local reporters.
"Some workers turned angry, destroying companies' gates and entering the compounds and asking other workers to join a strike."
The Council of Taiwanese Chamber of Commerce in Vietnam said the riots on Tuesday had caused big losses to Taiwan firms, among them Formosa Plastics Group, which said its unit's facilities in Dong Nai were damaged by looters..
China advised its citizens and businesses in Vietnam to take precautions.
"China's embassy in Vietnam once again reminds Chinese firms and staff in Vietnam to take security precautions and avoid unnecessary trips outdoors," the embassy said in a statement dated Tuesday on its website.
The rioters are believed to have mistaken Taiwanese firms for mainland Chinese-owned companies. Witnesses said those firms had put up signs declaring they were not Chinese.
The Formosa Plastics unit, whose shares are not listed, has invested $500 million building a petrochemical and fiber project last year, according to Taiwanese media.
The incident came after a weekend of rare rallies in Vietnam's biggest cities against China's actions.
The riots started with a protest on Monday by about 7,000 footwear and garment workers, who marched past Chinese businesses waving flags and demanding the removal of an oil drilling rig from near the disputed Paracel islands. Workers went on the rampage the next day, according to state media.
Pictures on social media showed smashed windows and plant pots, believed to be from the industrial park. Reuters could not independently verify the images.
Vietnam and China have has accused each other of ramming their ships near the Paracels over the past 10 days. The United States has called for restraint and described China of being provocative, prompting a rebuke from Beijing.
A police officer in Binh Duong province reached by telephone declined to give any new details but said an investigation was underway. A provincial state official overseeing industrial zones also declined to comment.
The People's Police newspaper, run by the Ministry of Public Security, said hundreds of policemen had been deployed to monitor the situation, stop those who incited the crowd, and protect corporate property.
It did not say if any arrests had been made.
Firms from numerous Asian counties, including China, Singapore, South Korea and Taiwan have set up shop in Binh Duong, which along with provinces of Dong Nai and Long An, form an industrial hub in southern Vietnam. (Reporting by Ho Binh Minh and Nguyen Phuong Linh and Faith Hung in Taipei; Editing by Martin Petty and Raju Gopalakrishnan)