Firefighters stand across from the main entrance of Tan Than Industries as the Taiwanese bicycle factory burns, in Di An Town, Binh Duong province, Vietnam, Wednesday, May 14, 2014. Mobs burned and looted scores of foreign-owned factories in Vietnam following a large protest by workers against China's recent placement of an oil rig in disputed Southeast Asian waters, officials said Wednesday. (AP Photo/Jeff Nesmith)

HANOI, Vietnam (AP) -- A 1,000-strong mob stormed a Taiwanese steel mill in Vietnam overnight, killing a Chinese worker and injuring 90 others, Taiwan's ambassador said Thursday, the first deadly incident in a wave of unruly anti-China protests prompted by Beijing's deployment of an oil rig in disputed seas.

The unrest is emerging as a major challenge for Vietnam's authoritarian and secretive leadership, and is hurting the country's reputation as a safe investment destination. It risks inflaming an already tense and dangerous standoff between patrol ships from both countries in the South China Sea close to the rig, which Hanoi is demanding Beijing withdraw.

Companies from Taiwan, many of which employ significant numbers of Chinese nationals, are bearing the brunt of the protests and violence, the most serious in years to hit the tightly controlled nation of 90 million people.

Taiwan's China Airlines has added two charter flights to its usual service to Ho Chi Minh city, making for a total of just over 1,000 seats for Taiwanese looking to leave Vietnam amid the unrest, according to Taiwan's Central News Agency.

The riot took place at a mill in Ha Tinh province in central Vietnam, about 350 kilometers (220 miles) south of Hanoi. It followed an anti-China protest by workers at the complex, operated by the conglomerate Formosa Plastics Group, one of the biggest foreign investors in Vietnam, according to Ambassador Huang Chih-peng and police.

Huang, who spoke to a member of the management team at the mill Thursday morning, said rioters lit fires at several buildings and hunted down the Chinese workers, but did not target the Taiwanese management. He said the head of the provincial government and its security chief were at the mill during the riot but did not "order tough enough action."

He said he was told one Chinese citizen was killed in the riots, while another died of natural causes during the unrest. He said around 90 others were injured. State-controlled online newspaper VnExpress quoted a top police official as saying that one Chinese person was killed, and that police and military troops had restored order.

A doctor at the Ha Tinh General Hospital said about 50 people, most of them Chinese nationals, were admitted to the hospital Wednesday night and early Thursday morning. He didn't give his name because he was not authorized to speak to the media.

Anti-Chinese sentiment is never far from the surface in Vietnam, but it has surged since Beijing deployed an oil rig into disputed waters about 240 kilometers (150 miles) off the Vietnamese coast on May 1. The government protested the move as a violation of the country's sovereignty and sent a flotilla of boats to the area, which continue to bump and collide with Chinese ones guarding the rig, raising the risk of conflict.

On Tuesday and Wednesday, mobs burned and looted scores of foreign-owned factories in southern Vietnam near Ho Chi Minh City, believing they were Chinese-run, but many were actually Taiwanese or South Korean. Authorities said they had detained more than 400 people.

Ambassador Huang said that the mill in Ha Tinh is Vietnam's largest foreign-invested project and that when completed it will be the largest integrated steel mill in Southeast Asia. It employs 1,000 Chinese nationals, he said. Vietnamese Prime Minster Nguyen Tan Dung attended the groundbreaking ceremony for the complex in 2012.

Low wages, especially compared to next-door China, and a reputation for safety, have been driving investment in Vietnam over the last years. But that was now at risk, said Minister of Planning and Investment Bui Quang Vinh.

He said 400 factories had been damaged since the unrest began this week, and that worker protests had broken out in 22 of the country's 63 provinces. "The investment image that we have been building over the past 20 years is turning very ugly," he told the parliament, according to an account in the state-run Labor newspaper.

Willy Lin, who heads a Hong Kong trade group representing knitwear manufacturers and exporters, said investors were hoping it was "one-off incident."

"If this madness continues and spreads out in the next couple of days to other parts of Vietnam, definitely it will have a very damaging effect on exporters, because they might not be able to commit to their delivery day," he said.

Hong Kong-based contract clothing maker Lever Style, which started outsourcing production to Vietnamese factories three years ago, has sent some Chinese quality assurance and technical support staff working at those factories back to China as a safety precaution, said CEO Stanley Szeto.

"You always have these little hiccups, no matter where you go," Szeto said. "Other than our staff, we're not really affected."

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Associated Press writer Kelvin Chan in Hong Kong contributed to this report.