HANOI, Vietnam — An anti-China march here in the Vietnamese capital on Sunday showed the domestic pressure the government faces when dealing with Beijing’s muscular approach to territorial claims in the South China Sea.

Scuffles broke out at the rally, which was a rare show of dissent in this tightly controlled one-party state, as the police hauled some 15 ringleaders or especially vocal protesters away in buses. “Down with the henchmen of China! Down with the traitors!” a detainee shouted through a window of the government bus taking him away.

Some members of the ruling Communist Party fear that popular anger over China, Vietnam’s ideological ally and biggest trading partner, could easily bleed into a broader protest movement against the government. The party already faces growing calls for reform because of economic malaise, corruption and the free spread of information critical of it over the Internet.

Sunday’s protest, which was advertised via blogs and Facebook pages, was in the heart of Hanoi around Hoan Kiem Lake, where many residents and foreign tourists gather Sunday mornings to walk and sip coffee in cafes.