Some 150 demonstrators staged a march in central Hanoi to mark the anniversary of a naval clash with China in which 64 Vietnamese sailors were killed.
The protesters waved banners and posters and chanted slogans during an hour long demonstration around Hoan Kiem Lake.
Despite their accustomed intolerance of public protest, the police did not intervene.
The activists denounced growing Chinese assertiveness in the disputed waters of the South China Sea and laid wreaths to commemorate the sailors killed in the clash around Johnson South Reef in 1988.
Some complained that the Vietnamese government was not doing enough to commemorate the battle, after which China took control of six reefs and atolls in the Spratly islands.
Militarising the dispute
The Vietnamese government has permitted more public discussion of the territorial dispute in recent years and occasionally allows small scale demonstrations against China’s claims.
Some activists suspect that the government is happy to see protests at the moment as a means of conveying its anger over China’s growing military presence in the disputed waters. The government, however, remains acutely sensitive about its ambiguous relations with China and activists are aware that they still risk arrest and possible imprisonment by taking to the streets.
Tensions with China in the South China Sea continue to increase, with the Vietnamese accusing Beijing of “militarising” the dispute with its suspected deployment of missile batteries on disputed islands, and the construction of air bases.
The Vietnamese government does not officially commemorate the clash in 1988.
The incident is, however, a touchstone for activists, who accuse China of invading Vietnamese territory. Some accuse the government of not doing enough to defend national sovereignty.
Many of the Vietnamese sailors were killed in the 1988 clash as they formed a ring, up to their chests in water, around a Vietnamese flag planted on Johnson South Reef in the Spratly chain.
In recent years China has built artificial islands on top of the partially submerged reefs and outcrops it occupied 28 years ago.
Three now have runways, which analysts say could be used to project Chinese air and naval power deep into waters that are also claimed by Vietnam, the Philippines, Malaysia, Taiwan and Brunei.