Vietnam on Sunday detained about 30 anti-China protesters in Hanoi, witnesses said, amid growing tensions between the communist neighbours over rival territorial claims.
Security forces moved in to disperse about 100 demonstrators who gathered in the city centre for an hour-long rally, witnesses said.
The detained were taken by bus to a “rehabilitation” centre on the outskirts of the capital.
Two AFP journalists covering the demo were among those detained but were released after a few hours.
Vietnam and China have long-standing territorial disputes over the Spratly and Paracel Islands, which both countries claim, and often trade diplomatic barbs over oil exploration and fishing rights in the contested waters.
In March Hanoi accused a Chinese vessel of firing on one of its fishing boats.
Last month Beijing sent one of its largest recorded fishing fleets to the disputed waters.
More than a dozen anti-China demonstrations have been held in Vietnam since 2011. After initially tolerating the rallies, the Vietnamese authorities have since banned them.
Vietnamese Prime Minister Nguyen Tan Dung, speaking at a security conference in Singapore, on Friday slammed “groundless” territorial claims in Asian waters and called for self-restraint among nations involved in disputes.