Hanoi has accused Chinese sailors of attacking a group of Vietnamese fishermen near a disputed island chain, the latest in a string of maritime spats between the communist neighbours.

Vietnam's Foreign Ministry said the vessels were fishing in waters around the Paracel Islands -- claimed by Vietnam but controlled by China -- when they were attacked.

They were stopped by Chinese sailors in speedboats who "prevented them fishing and took away their equipment... some sailors were beaten," the foreign ministry said in a Tuesday statement, without giving further details.

Vietnam has demanded China investigate the incident and punish those responsible, ministry spokesman Le Hai Binh said.

China and Vietnam, once close ideological allies, are locked in a bitter territorial wrangle over waters and island chains in the South China Sea.

In May, Beijing moved a deep-sea oil rig into waters that Hanoi claims, sparking deadly anti-China riots in Vietnam and triggering a standoff around the rig.

Beijing removed the rig in July, claiming its mission was successfully completed.

A month later Chinese President Xi Jinping told a top Vietnamese envoy that the two countries should repair strained ties.

China claims nearly all of the South China Sea, even waters approaching the coasts of its neighbours, and has become increasingly assertive in staking those claims.

Vietnam, the Philippines, Brunei, Malaysia and Taiwan have competing claims to parts of the sea.

Vietnam's authoritarian leaders have struggled to balance traditionally warm ties with fellow communists in Beijing with widespread anti-China sentiment among the population.