Vietnamese police on Thursday scuffled with activists marking the 1974 Chinese invasion of a disputed island chain as they arrested several people and dispersed journalists.

About 100 people gathered in central Hanoi for the 43rd anniversary of the Chinese takeover of the Paracel islands in the South China Sea -- territory claimed by both nations that remains a diplomatic flashpoint.

In a rare act of public defiance in the communist nation, activists chanted "Down with the invaders!" and held banners against the "age-old enemy" near the capital's Hoan Kiem Lake.

Plainclothes police swiftly swooped in, snatching banners away and hauling at least a dozen people into a nearby bus.

Journalists were unceremoniously ordered to leave the scene and turn off cameras.

Though Hanoi and Beijing routinely trade barbs over contested territory in the South China Sea, Vietnam often breaks up anti-China protests to avoid stoking anger from regional powerhouse China.

The Paracels remain a bitter bone of contention between the neighbours.

China has controlled the islands since invading them shortly after US-backed Vietnamese soldiers withdrew in 1974.

The attack left 70 Vietnamese soldiers dead.

Activists called on Vietnam to take a tougher stance with China.

"I think Vietnam must be determined towards China... to get back Hoang Sa and Truong Sa Islands," said activist Pham Van Troi, 46, using Vietnamese names for the Paracels and the nearby Spratly islands, which are also disputed.

Beijing lays claim to virtually all of the South China Sea, and has built up islands capable of hosting military installations.

The Philippines, Vietnam, Malaysia, Brunei and Taiwan have also sparred with Beijing over territory in the disputed waterway.

Tensions have eased slightly in recent months but the issue remains a potential global flashpoint.

In 2014 China moved a controversial oil rig into contested territory, prompting deadly riots in Vietnam.

Last week Chinese state media reacted with fury to comments by US secretary of state nominee Rex Tillerson that he would seek to deny Beijing access to the artificial islands it has built up in the contested sea.