The risk of AIDS spreading in Asia is higher than ever and there is a danger of an "explosion" of the deadly disease if prevention efforts are not intensified now, the top United Nations AIDS official said on Friday. One in four new infections occurs in Asia, with the disease having spread to all provinces of China amid its economic boom and India with the world's second-highest number of AIDS/HIV patients after South Africa. World health officials and AIDS activists called for increased prevention efforts and access to cheap medicine as an international Asia-Pacific AIDS conference opened in the western Japanese city of Kobe on Friday, emphasizing the need for increased political will to fight the epidemic -- which they said is often lacking in Asia in particular. Japan's health minister, scheduled to attend, was unable to make it. A ministry official gave his speech instead. In Asia, the AIDS epidemic is still mainly found among vulnerable groups such as homosexuals, injecting drug users and sex workers, but it could spread to the general population unless intense efforts are made, said Peter Piot, executive director of UNAIDS, the U.N. agency devoted to fighting the epidemic. "When I look at what's going on in many countries in Asia there's a vicious cocktail of risk factors," Piot told Reuters before the conference began. "An explosive cocktail of risk factors that mean that if 'business as usual' continues there will undoubtedly be an explosion of AIDS," he added. --more 1357 Local Time 1057 GMT