Military and political tensions in the South China Sea are threatening the development of Asia's burgeoning cruise holiday market, shipping and travel experts say. Dr Liu Zinan, chairman of the Asia Cruise Association, said the Sino-Japanese dispute over the Diaoyu Islands was "having an adverse impact on us". Liu, who is also regional vice-president for Asia for Royal Caribbean Cruises, said Beijing had relaxed travel restrictions, but for the "foreseeable future we can't make the best use of the government permits", especially when it came to "itineraries to Taiwan and Japan". He said any discussion about developing cruise itineraries in the South China Sea had to take into account geo-political issues. "Unfortunately they come to [affect] us again and again," he told delegates to the Seatrade Hong Kong Cruise Forum yesterday. Either people would be deterred from travelling or the threat of military action would curtail voyages between China, South Korea and Japan. The cruise association represents about 40 organisations including cruise, port and tour companies and tourism authorities. His views were echoed by Pier Luigi Foschi, chairman and chief executive of Carnival Asia, who said the negative impact was starting to be felt now as cruise lines planned their Asian port and country calls. Worsening relations between China and Japan, which saw violent demonstrations and flag burnings in several mainland cities, did not have a big impact last year because they coincided with the end of the cruise holiday season. But Foschi said continuing poor relations was "going to affect business beginning this year". Speaking on the sidelines of the conference, he said the problems, particularly between China and Japan, was "limiting the choice of itineraries". Asked if rising tensions between China and Vietnam was a concern, Phan Xuan Anh, president of leading Vietnamese tour company Viet Excursions, said: "Not yet, but it could be." Anh pointed out that there was unease in Vietnam about China's ambitions in the South China Sea. Disputes have centred on offshore oil and gas exploration off the coast of Vietnam and territorial wrangles over the Spratly Islands. These worries come amid a forecast "supersonic" growth in the number of Asian, especially mainland Chinese, cruise passengers. Foschi expected there would be seven million cruise ship passengers from Asian countries by 2020, accounting for more than 20 per cent of the global cruise market. "I could be wrong, it could be 10 million," he said, adding: "Asia is too big to ignore".