THE detention of the Hong Kong-based Ming Pao reporter Xi Yang is a clear warning to journalists and cadres not to go too far in disclosing information the central Government wants kept under wraps or held pending official release. The crackdown against what the communist regime saw as serious leaking of official information was aimed both at journalists and cadres who have had access to state documents. Only in August, a People's Daily editor was sentenced to life imprisonment for selling a ''most secret document'' to a reporter from the Hong Kong-based Express during the Communist Party's plenum last year. The Hong Kong reporter, Leung Wai-man, was detained and then released. Her penalty was a two-year ban from going to China. Xi was arrested on charges of ''espionage regarding state secrets on banking''. Xinhua (the New China News Agency) said Xi had violated state security laws, but gave no details of his alleged activities. His colleagues in Ming Pao said they had no idea what ''state secrets'' Xinhua was referring to. A veteran mainland editor believed the ''state secrets'' might be information Xi had collected during his present trip to Beijing. ''At the centre of the incident might not be what he has written or published by Ming Pao in the past, but what he has got and might prepare to write,'' he said. He noted that Xi and two of his colleagues had been given a full interview with Deng Pufang, the elder son of patriarch Deng Xiaoping, in Beijing last week. ''Xi Yang would not have been given the interview if Beijing wanted to punish what he has written in the past.'' Analysts say Beijing has been imposing tighter control over the flow of information to make sure that those on the mainland will not provide information to people from outside the country. Ming Pao, one of Hong Kong's most respected Chinese-language newspapers, has given prominent coverage to the mainland's financial traumas, including the top-level shake-up in the People's Bank of China in July. One sensitive report covered the removal of the former bank chief Li Guixian and the appointment of Vice-Premier Zhu Rongji as the new bank governor. Detailed first-hand reports on the national financial work conference from July 5 to 7 and the conference among heads of foreign exchange bureaus in August were also published. Xinhua also carried reports on the reshuffle and the conferences. Analysts said it was hard to see how media reports on China's banking restructuring had endangered national security. The central leadership has ordered cadres at all levels to give full support to central orders, including the austerity programme and anti-graft campaign. Any leaking of official information will be seen as a challenge to the authority of the ruling party.