Mobs chanting anti-Chinese slogans have set at least 15 foreign factories on fire in southern Vietnam.

An analyst said the incidents were among the country's most serious riots and would tarnish its image as an investment and tourist destination.

The rioting started late on Tuesday when about 19,000 workers protested at a Singapore-run industrial park and others nearby in Binh Duong province, 1,120 km south of Hanoi, the capital.

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Authorities said rioting and looting forced the closure of 1,000 factories, but no casualties were confirmed. About 500 people were arrested.

The incidents came after anti-China street protests over the weekend following Beijing's recent deployment of an oil drilling rig in its territorial waters in the South China Sea, which are also claimed by Vietnam.

In a phone conversation with his Indonesian counterpart on Wednesday, Foreign Minister Wang Yi said China wanted Vietnam to calm the situation.

"China's stance of protecting its legal sovereign rights is firm, clear and will not change," he said.

Ministry spokeswoman Hua Chunying said Beijing had lodged protests with the Vietnamese ambassador, asking the Vietnamese "to immediately take effective steps to stop and punish these crimes, and to ensure the safety of Chinese citizens and institutions in Vietnam."

Hua said Hanoi had deliberately escalated tensions by allowing its vessels to ram Chinese boats around the rig on 169 occasions on Tuesday and by arranging for reporters to cover the process.

"This was all done for show in an attempt to present a false picture and deceive the public," she said.

Li Jinming, a Xiamen University professor of maritime law and South China Sea studies, said, "Vietnam is provoking China on land and sea in a high-stakes gamble."

Tran Van Nam, deputy head of the province's people's committee, was quoted by VnExpress as saying that the protests were initially peaceful but had been hijacked by extremists who incited people to break into the factories.

Hundreds of other factories were vandalized or looted, while some security guards and technicians were assaulted, the official said.

He said people attacked factories they believed were run by companies from the Chinese mainland, but some were run by people from Taiwan, Japan or South Korea.

On Wednesday morning, nearly all the factories in the area were closed and riot police had been deployed.

Global exporter Li & Fung, which supplies retailers such as Kohl's Corp and Wal-Mart Stores with clothing, toys and other products, said it had suspended production in Vietnam.

Yue Yuen Industrial Holdings, a Taiwan manufacturer with headquarters in Hong Kong, also suspended production. It makes footwear for firms including Nike and Adidas.

Vietnamese Internet users have questioned the motivation and impact of the rioting.

"Young people should be more cautious and avoid being used by bad people. The (foreign) companies have brought jobs — what is wrong with them?" a netizen nicknamed muoihcm commented in the VnExpress report.

The Vietnamese government gave rare permission for the weekend protests, which were enthusiastically covered by state media.

Li Guoqiang, deputy director of the Research Center for Chinese Borderland History and Geography at the Chinese Academy of Social Sciences, said, "It is high-profile propaganda for the Vietnamese authorities and media regarding the collision of ships in the South China Sea that enraged public opinion and resulted in the riots.

"The incident will not only harm relations with China but also endanger Vietnam's international image, especially as an investment and tourist destination."

Wang Jian and Xinhua contributed to this story.