HANOI, Vietnam -- More than 400 people were arrested after riots in which scores of foreign-owned factories were damaged or destroyed in an industrial area in southern Vietnam, authorities said Wednesday.
The upheaval Tuesday was the worst public unrest in recent Vietnamese history, involving thousands of workers. It reportedly began as demonstrations against China's stationing of an oil drilling rig in disputed waters off Vietnam's coast. But the protests boiled over into widespread violence, as workers rampaged through a dense industrial area in a northern suburb of Ho Chi Minh City, once known as Saigon. The area has rows of cavernous buildings where thousands of mostly young workers stitch together sneakers and clothing for sale around the world.
"No one knows what really caused the riots -- only initially did it seem to be about the Chinese," Truong Huy San, an author and well-known blogger, said by phone after touring the industrial zone. "These were totally uncontrolled crowds."
The great majority of the affected factories and workshops were owned by Taiwanese or South Korean companies.
"There was quite a lot of damage," said Chen Bor-show, director-general for the Taipei Economic and Cultural Office, which functions as Taiwan's de facto consulate in Ho Chi Minh City. Mr. Chen said around 200 Taiwanese companies were affected.
The South Korean Foreign Ministry said 50 Korean-owned factories were damaged in the riots, and one South Korean citizen was hospitalized with injuries that were not life-threatening.
Mr. San, the blogger, who uses the pen name Huy Duc, said some of the workshops were severely damaged.
"It's kind of a disaster zone," he said. "Everyone is scared. There are hundreds of factories that will have to close for weeks or months."
Mr. San said the riots were a signal to Vietnam's authoritarian government that workers needed avenues to express their grievances. Independent unions are banned in Vietnam.
"I don't know whether the government recognizes the very important message that was sent from this province," he said. "The government needs to do something to change their thinking and policy."
Tran Van Nam, vice chairman of Binh Duong province, where the violence occurred, was quoted by a Vietnamese online news site, VNExpress, saying around 19,000 workers were involved in the protests Tuesday.
Another provincial official, Tran Xuan Nam, said in a phone interview late Wednesday that the situation there was "stable," and that 447 suspects had been detained.
"We will restore order as soon as possible," he said. Mr. Nam said 20 factories had been "seriously destroyed." He attributed the riots to "extremism," but did not elaborate.
The Chinese Embassy in Hanoi issued a warning Wednesday to Chinese citizens in Vietnam, urging them to "minimize unnecessary outings." The Hong Kong government posted a travel alert, warning residents to "avoid protests and large gatherings of people."
The business effects of the riots were not immediately clear.
Yue Yuen, a Taiwan-based company that manufactures shoes for Nike, Adidas and other brands, said it had given its workers in Vietnam the day off Wednesday, and had not yet decided whether to reopen today, even though its factories were not damaged, and none of its workers was injured.
Jerry Shum, the company's head of investor relations, said Yue Yuen expected calm to return quickly to industrial districts in the country, and believed that it could still meet its monthly production targets.
The maritime dispute between China and Vietnam, the ostensible spark for the protests, began in early May, when China towed a huge drilling rig to a spot in the South China Sea 140 miles off the coast of Vietnam and about 17 miles from a small coral atoll claimed by both countries. Each side sent ships and boats to the area, and there were several confrontations and collisions last week, with each side blaming the other.