Anti-China protesters set several Chinese- and Taiwanese-owned factories on fire and looted hundreds of others on Tuesday night in southern Vietnam amid rising tension over China’s recent deployment of a giant oil rig in a disputed portion of the South China Sea, officials and state media said Wednesday.

The unrest erupted on Tuesday when more than 20,000 workers at industrial complexes in Binh Duong province, which lies north of Ho Chi Minh City, protested Beijing's deployment of an oil drilling rig in the South China Sea. At least 15 factories were set alight and hundreds more were looted, while some security guards and unidentified "foreign experts" were assaulted, according to Tran Van Nam, deputy head of the province's people's committee, VnExpress reported. Companies doing business in Vietnam are estimated to have lost billions of dollars after their factories were damaged in the violence.

“The workers are not choosing from which country the factory belongs,” Bob Hsu, general manager of Taiwan’s Great Super Enterprise Ltd., told Bloomberg. Protesters looking at company names “are just trying to find a Chinese word. It includes Korean, Japanese factories.”

The Vietnamese government has mobilized riot police and military forces to handle the aftermath on Wednesday, while all factories in the area remained closed. The recent unrest at industrial parks established to attract foreign investors is one of the most serious outbreaks of public disorder in the tightly controlled country in years.

The Chinese embassy in Hanoi reportedly issued a notice Wednesday urging Chinese people living in Vietnam to “minimize unnecessary outings,” and asked Chinese firms to take security precautions against possible violence.

A Taiwan-based employee of Canada-based Asama Bicycles, whose factory was damaged in the riot, told CNN that "all personnel have been evacuated from the factory and we can only learn the situation after the protesters leave the area."

Vietnam reacted angrily after China towed a deep-sea oil rig earlier this month close to the Paracel Islands, which are controlled by China but claimed by Hanoi, while some Vietnamese boats sent to intercept the oil rig were reportedly rammed by Chinese ships.

In a statement issued last week, the U.S. Department of State called China's decision of sending the oil rig, accompanied by a flotilla of government vessels, "provocative" and an act that "raises tensions."

"This unilateral action appears to be part of a broader pattern of Chinese behavior to advance its claims over disputed territory in a manner that undermines peace and stability in the region," the statement said.