HANOI - Anti-China protesters have set more than a dozen factories on fire in Vietnam in the biggest eruption of rage against Beijing for years over the deployment of an oil rig in contested waters.
China expressed "serious concerns" after Vietnamese workers looted goods and attacked offices Tuesday in a rare outburst of public unrest in the authoritarian communist nation.
The protesters targeted manufacturing companies that are owned or managed by Chinese as well as Chinese experts in Binh Duong province, the Vietnam Singapore Industrial Park said in a statement.
There were no reports of casualties but the violence forced several factories to temporarily suspend operations. Many of the those affected were Taiwanese and South Korean-owned plants, possibly mistaken to be Chinese-owned.
Police detained 500 people "caught red-handed looting, stealing and setting fire to factories," Le Xuan Truong of the Binh Duong police told AFP.
Hanoi usually tightly controls demonstrations but recently allowed mass rallies against Beijing.
The riots show the "hazards of nationalist fervour unleashed, particularly in repressive institutional environments such as Vietnam," said Professor Jonathan London at City University of Hong Kong.
"Nationalist sentiment of the intensities we observe in Vietnam are difficult to manage from the top down," London told AFP.
Tens of thousands of workers poured onto the streets Tuesday and a small number of them began looting and attacking security guards and factory management before setting fire to at least 15 factories, the state-run VNExpress website reported.
Videos and images posted on dissident blogs showed thousands of workers - many waving the Vietnamese flag - destroying factory gates, smashing windows and damaging offices.
Export-orientated manufacturing is a key pillar of Vietnam's economy with high-profile firms from electronics giants such as South Korea's Samsung to US sportswear companies Nike and Adidas producing goods in Vietnam.