HANOI, May 15 -- Around 10 Chinese remained unaccounted for on Thursday after violent rioters attacked Chinese companies in Vietnam's central Ha Tinh Province, with casualties feared, sources said.

"The protests were held throughout Wednesday. The rioters attacked our four Chinese companies constructing an iron and steel complex invested by China's Taiwan," a Chinese manager in Ha Tinh, which is some 300 km south of Vietnamese capital Hanoi, told Xinhua.

"They broke into our offices, wrecking and looting the properties, and burned our dormitory building before leaving," he said, requesting anonymity for fear of retaliation.

Among the four Chinese companies there, China 19th Metallurgical Corporation (MCC19) was the most seriously hit.

"So far, around 10 staff lost contact with us and at least 55 workers were wounded," an official with MCC19 told Xinhua on Thursday morning.

"The security forces here were far less enough, leaving our workers and the Vietnamese policemen badly attacked before two o'clock this morning," he added.

Nguyen Minh Hoan, vice chairman of the People's Committee of Ky Anh District in Ha Tinh Province, where the bloody attacks occurred, told Xinhua over phone that he had just attended a meeting on the violence.

But he refused to give any figure of the casualties, saying the Ha Tinh Province was expected to make an official announcement on Thursday afternoon.

The senseless anti-China attacks in Vietnam came amid rising tensions between the two countries over their territorial disputes after Vietnamese ships and personnel repeatedly harassed the normal operations by a Chinese oil company in undisputed waters in the South China Sea.

Vietnamese Prime Minister Nguyen Tan Dung on Thursday ordered the Ministry of Public Security to ensure security and absolute safety for lives and assets as well as normal operation of all companies, especially foreign invested firms.

According to the directive on Vietnamese government's website, the prime minister urges unanimous, active and firm measures to be implemented to prevent illegal activities and strictly handle those who had provoked riots.

The directive asked local people not to follow illegal actions, in order to ensure security and solidarity and contribute to economic development.