HANOI (AP) ― A 1,000-strong mob stormed a Taiwanese steel mill in Vietnam overnight, killing a Chinese worker and injuring 141 others, Taiwan’s ambassador and police 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 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. In his first remarks on the crisis, Vietnamese Prime Minister Nguyen Tan Dung said peaceful protests over the last few days were “legitimate,” but that anyone involved in violence should be punished severely.

“This is serious,” he said in a telegram to police across the country.

Nervous Chinese expatriates were fleeing by land and air. Cambodian immigration police said 600 Chinese crossed into Cambodia over the land border in southern Vietnam on Wednesday, and that others were arriving Thursday.

Taiwan’s China Airlines was adding two additional charter flights from southern Vietnam‘s Ho Chi Minh city, according to Taiwan’s Central News Agency.

The riot took place at a mill in Ha Tinh province in central Vietnam, about 350 kilometers 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. Ha Tinh‘s deputy police chief, Bui Dinh Quang, said the situation was “stable” on Thursday and that none of the injured, which he put at 141, had life-threatening injuries.

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 off the Vietnamese coast on May 1, close to the Paracel Islands. The government protested the move as a violation of Vietnam’s sovereignty and sent to the area a flotilla of boats, which continue to bump and collide with Chinese vessels guarding the rig.