China and Vietnam want to discuss joint development of the South China Sea, state media reported on Saturday as Vietnamese communist party head Nguyen Phu Trong wrapped up a visit.

The potentially oil-rich waters are at the centre of a territorial dispute between the neighbours.

"The leaders of the two (communist) parties and countries will keep frequent communication and dialogue on the maritime issues," according to the text of a joint statement quoted by Xinhua news agency.

"Both sides will seek steady progress in negotiations regarding the maritime demarcation of the bay mouth of the Beibu Gulf (Gulf of Tonkin) and discuss the joint development of the sea area," the statement said.

"Neither side shall allow any hostile force to destroy the relations between the two parties and the two countries," it said.

China and Vietnam have a long-standing dispute over sovereignty of the Paracel and Spratly island groups, which are in oil-rich waters straddling vital commercial shipping lanes in the South China Sea.

In July a Chinese warship confronted an Indian naval vessel in waters off Vietnam and demanded it to explain its presence.

China says it has sovereignty over essentially all of the South China Sea, a key global trading route, where its professed ownership of the Spratly archipelago overlaps with claims by Vietnam, the Philippines, Taiwan, Brunei and Malaysia.

Vietnam and the Philippines have reported a rising number of incidents with China, citing in particular harassment of their fishermen by Chinese vessels.

The United States also made an appeal for calm Friday after reports that Taiwan was preparing to deploy missiles in the South China Sea.

Beijing routinely rejects US "interference" in the region and says it intends to resolve its territorial disputes on a bilateral basis with the countries concerned.

Trong's visit to China was his first since he was appointed in January as secretary general of the Communist Party of Vietnam.

The two communist countries, which fought a brief border war in 1979 before normalising relations in 1991, also agreed to strengthen cooperation against illegal border crossings, Xinhua reported.