China and Vietnam maintain rival claims across swathes of the South China Sea, including the Paracel Islands. Called the Xisha islands in Chinese, they are a cluster of close to 40 islets, outcrops and reefs that are controlled by Beijing.

That dispute and a mosaic of other conflicting claims have set China against Vietnam, Brunei, Malaysia, the Philippines, and Taiwan.

The proposed opening of the Paracel Islands to tourism could add to the long-standing friction, which has drawn the United States into pressing China over the issue.

The Japanese-built ship carried out a three-day voyage to the northern shoals of the Paracels, the official Xinhua news agency reported, though it added there was no firm timetable for a launch of such cruises.

Initial plans call for ships to visit Woody Island, called Yongxing Island by China, though tourists would not be allowed to leave their boat.

"They will tour around the northern shoals of Xisha, enjoying the awesome views and the blue sea, before returning to Hainan," said Huang Peng, an official with the transport bureau of Hainan, China's southern island-province that is near the disputed islands.

"For the next stage, we will build bigger ships and make other improvements to meet the demands of high-end customers," Huang told the Xinhua news agency.

Tourism to the Paracels is important as "it is a declaration of sovereignty over the islands ... that have been a part of Chinese territory since ancient times", the official added.

Deng Zhonghua, head of the Foreign Ministry's department of boundary and ocean affairs, told a question and answer session on the People's Daily website that China was perfectly in its rights to allow tourism to the Paracels.

"This is a matter which is completely within the scope of China's sovereignty, and no other country has the right to interfere," he said.

China has given conflicting signals on its plans for the islands. State media last week denied an earlier report the government planned to let tourists visit the Paracels.

Last month, China and Vietnam quarrelled after Beijing said it had detained 21 Vietnamese for illegal fishing around the Paracels but Vietnam said the fishermen had been detained in its waters and demanded their immediate release.

Tension has risen in the region in the past two years over concern that China is becoming more assertive in its claim to the seas, believed to be rich in oil and gas and straddling shipping lanes between East Asia and Europe and the Middle East.

(Reporting by Ben Blanchard and Chris Buckley; Editing by Robert Birsel)

• A Permanent Economic Emergency