Dozens of Vietnamese who gathered for an anti-China protest in central Hanoi were taken away by authorities Sunday as they tried to rally support for an international tribunal's ruling rejecting Beijing's claims in the South China Sea.

About two dozen people were bused away from around the landmark Hoan Kiem Lake in Vietnam's capital even before they began their protest. There was a heavy police presence around the lake, with cars briefly banned from around it.

The rally was organized by No-U, a Hanoi group that opposes China's expansive claims in the South China Sea. It came after the Hague-based Permanent Court of Arbitration issued the ruling last week in a case initiated by the Philippines, which together with Vietnam is one of the claimants in the disputed waters.

China rejected the tribunal's ruling and refused to take part in the arbitration.

The tribunal ruled that China violated international maritime law, specifically the Philippines' maritime rights, by building up artificial islands that destroyed coral reefs and by disrupting fishing and oil exploration.

Nguyen Chi Tuyen, a member of No-U, said the activists who were detained by police were all released by early Sunday afternoon.

Another small group of activists gathered in front of the Philippine Embassy in Hanoi at around noon with banners that read "Thank you, Philippines, you have a brave government" and "China, you must comply with international law," Tuyen said.

Vietnamese authorities have clamped down on such protests before, fearing they could stir dissent in the communist country.