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.