HANOI - Thousands of workers staged a protest at an industrial park in southern Vietnam yesterday over China's deployment of a drilling rig in contested waters, damaging factories and offices, official media said.

Photos posted on the official news site of the Ministry of Information showed what appeared to be extensive damage to a Taiwanese factory that was apparently mistaken for a Chinese-owned plant.

Local policeman Ho Quang Thanh said the protest in Binh Duong province was triggered by the row over the oil rig, which Beijing moved into disputed waters this month to Vietnam's dismay.

Hanoi has branded the move as "illegal" and dispatched vessels to the area. China and Vietnam are locked in longstanding territorial disputes in the South China Sea over the Paracel and Spratly islands, which both claim.

There have been repeated skirmishes near the oil rig in recent days involving vessels from both countries, with collisions and the use of water cannon. Beijing has accused the United States of emboldening Asian nations in their territorial disputes with China.

On Sunday, Vietnamese protesters staged multiple, large anti-China demonstrations with at least 1,000 people gathering in Hanoi and a similar-sized crowd in Ho Chi Minh City.

There have been multiple calls by Vietnamese Internet users for further protests. Dozens of anti- China demonstrations have been held in Vietnam since 2007 to protest against Beijing's perceived aggression over territory.

Attacks on foreign-backed factories, which are a key part of Vietnam's economy, mark an escalation of the public backlash.

Vietnam has alternated between tolerating the rallies and violently breaking them up. The communist regime is wary of public gatherings that could threaten its rule.

Experts say Vietnam's leadership has allowed some protests to go ahead as a means of expressing extreme discontent with Beijing. Vietnam's tightly controlled state media has been granted permission to report on the protests and given access to the Vietnamese ships close to the Chinese oil rig.

AGENCE FRANCE-PRESSE