HANOI, Aug 21 (Reuters) - Vietnamese police detained scores of people taking part in an anti-China rally in Hanoi on Sunday in defiance of a government order to end a string of demonstrations that has stretched three months and put authorities on edge.
One witness said plainclothes police forced around 40 demonstrators onto two public buses and drove them away within minutes of the start of the demonstration. A blogger who has chronicled the demonstrations and has contacts among the regular protesters said at least one bus left with 19 people aboard.
It was the 11th anti-China rally in an unprecedented series of public protests that have taken place nearly every Sunday since early June against what Vietnamese see as China's violations of their country's sovereignty in the South China Sea.
"We're very concerned that protesters were arrested by the police and call for their immediate release," said Phil Robertson, deputy head for Asia of Human Rights Watch.
"Sadly, the over-reaction of the authorities was shown by the fact that the police outnumbered the protesters, and their aggressive actions to prevent the assembly from going forward. These protesters have done nothing wrong, the police should release them unconditionally."
The Hanoi city government on Thursday had issued an order to end "gatherings, demonstrations and spontaneous marches" and threatened to take "necessary measures" against those who defy the order.
In response, 25 prominent intellectuals and others connected to the demonstrations wrote a petition to the Hanoi People's Committee saying the order was unconstitutional. The letter was posted online.
The anti-China demonstrations started after the Vietnamese government made public a case in late May in which it said Chinese patrol ships harassed a Vietnamese seismic survey ship operating in Vietnamese waters.
In addition to Vietnam and China, four other nations -- Brunei, Malaysia, Taiwan and the Philippines -- also have competing claims to parts of the South China Sea.
The Hanoi government notice on Thursday said they were interfering with diplomatic efforts in the dispute with China.
The demonstrations have so far not exceeded 300 people, but Vietnam's Communist Party brooks no opposition and analysts say it is nervous about Arab-style protests against autocratic rule.
The blogger, Nguyen Xuan Dien, said police had several people in recent days to urge them to refrain from participating in the protests. Another activist who declined to be identified said "scores" of people had been confined to their homes or otherwise hindered from attending on Sunday. (Reporting by John Ruwitch, editing by Miral Fahmy)