Vietnamese police rounded up at least 10 people as they broke up an anti-China rally on Sunday for the second weekend running after a series of protests over tensions in the South China Sea. Around 50 demonstrators, greatly outnumbered by security forces, were stopped and forced to disperse after they gathered close to the Chinese embassy in the capital Hanoi. "Down with China! Down with arresting patriotic people!" shouted the protesters as they waved banners denouncing Chinese "violations" of Vietnamese sovereignty. It was the seventh in an unprecedented series of protests -- uncommon in authoritarian Vietnam -- that have taken place in Hanoi on recent weekends during an escalating maritime dispute in the South China Sea. Authorities in Hanoi allowed the first five protests to proceed without incident, but briefly detained 10 people, including journalists, during a rally on July 10 after talks with China in Beijing. The communist neighbours have long been at odds over the potentially oil-rich Paracel and Spratly island groups, which straddle vital commercial shipping lanes in the South China Sea. At their June 25 meeting, both sides agreed to resolve their territorial disputes peacefully. Beijing and Hanoi "also laid stress on the need to steer public opinion in the correct direction", the official Vietnam News said. Human Rights Watch criticised the "latest wave of arrests and violence against peaceful demonstrators". "These protesters should not have been arrested in the first place and the authorities should release them immediately without conditions," said Asia division deputy director Phil Robertson. Tensions flared in May when Vietnam said Chinese marine surveillance vessels cut the exploration cables of an oil survey ship and Hanoi has accused its neighbour of harassing Vietnamese fishing boats in the disputed waters. On Friday, Vietnam and the United States began a joint naval drill in the South China Sea despite Chinese objections.