BEIJING (AFP) - Beijing on Thursday accused Hanoi of acting in concert with anti-China protestors who have killed at least one Chinese citizen in demonstrations against the deployment of an oil rig in disputed waters.

The violence in Vietnam had "a direct link with the Vietnamese side's indulgence and connivance in recent days with some domestic anti-China forces and lawbreakers", Beijing's foreign ministry spokesman Hua Chunying told reporters.

China's official news agency Xinhua said that around 10 Chinese remained unaccounted for after rioters attacked four Chinese companies in the central province of Ha Tinh, citing a Chinese manager.

"So far, around 10 staff lost contact with us and at least 55 workers were wounded," it quoted a representative of the worst-hit firm, China 19th Metallurgical Corporation, as saying.

Xinhua also quoted an unnamed Chinese company manager as saying: "The protests were held throughout Wednesday. They broke into our offices, wrecking and looting the properties, and burned our dormitory building before leaving."

At the foreign ministry, Hua declined to say how many Chinese had died in the protests, but said Chinese diplomatic officials were en route to the scene to find out more.

"We have launched solemn representations with Vietnam," she said, urging Vietnam to take responsibility, seriously punish the lawbreakers and compensate Chinese citizens and firms.