The apparent secretive visit of North Korea's reclusive leader, Kim Jong-il, to his closest ally China on Tuesday, after a visit by President Hu Jintao to Pyongyang in October last year, underscores the close ties between the two nations. But analysts say the mainland's political influence over its mercurial neighbour is not as strong as many in the administration of US President George W. Bush had hoped, and that Beijing would, in any case, be unwilling to exercise what leverage it does possess on Washington's behalf. Other experts contend that contrary to Pyongyang's fierce - and frequently reiterated - claims of self-reliance, the near-bankrupt regime is on its way to becoming a virtual economic colony of China. Citing unnamed sources, South Korea's semi-official Yonhap news agency said Mr Kim, amid tight security, passed through the Chinese border town of Dandong on his personal train and arrived in Beijing at 4pm on Tuesday. Neither capital has confirmed the visit. On Mr Kim's last visit, in 2004, Beijing only confirmed a summit had occurred after he had departed. While Yonhap did not speculate on the reason for the visit, the stalled six-party talks on North Korean nuclear disarmament are likely to top any agenda. Analysts say Mr Kim might also be hoping to underscore the bilateral alliance, discuss economic reforms, seek support against Washington's financial sanctions, and possibly discuss an economic aid package. A range of administration figures in Washington, as well as from right-wing think tanks, have called publicly on Beijing, the sponsor of the six-party talks, to do more to bring Pyongyang to heel. But while China has made diplomatically couched recommendations to North Korea, experts in Seoul are sceptical as to whether Beijing has the appropriate leverage to force the regime to undertake policies - or would employ such leverage if it had it. 'China has more influence than Chinese authorities like to admit, although less than the rest of the world thinks. But there is an expectation in the US that it could tell North Korea what to do,' said Peter Beck, the Seoul-based Northeast Asia director of think tank the International Crisis Group (ICG). 'But China's top concern is stability.' Although China is North Korea's main trade partner, few expect China would kowtow to US pressure and cut trade or aid to spur progress in nuclear talks. 'Nothing would convince them to use their leverage,' said Choi Jin-wook of Seoul's Institute of National Unification. 'I don't think China will try to cut trade at the risk of killing North Korea. Of course, it is influenced by the US, and China said it does not tolerate North Korea's nuclear programmes, but it does not want North Korea to collapse.' China already faces international criticism for forcibly repatriating North Korean refugees in China - numbered at between 100,000 and 300,000 - to their homeland, where they reportedly face severe penalties. Heightened instability there would drive much larger numbers across the 1,000km frontier. 'They don't want border instability,' said Moon Chung-in, a foreign policy expert at Seoul's Yonsei University and adviser to South Korean President Roh Moo-hyun. 'China's basic tenets of foreign policy are to make friendly relations with their neighbours, make them rich and keep them stable. Historically, tranquility on the periphery is important for stability of the centre.' Nor is there any indication that Beijing is willing to pressure Pyongyang. In 2004, mainland journal Strategy Management suggested a closer alignment with Washington, at the expense of the Pyongyang relationship. The magazine, known for controversial viewpoints, was shut down. China also maintains a 1961 friendship, co-operation and mutual assistance treaty with North Korea - which, on paper at least, places Beijing on Pyongyang's side in any military confrontation with Washington. The old guard in the Chinese Communist Party remember the 'blood alliance' forged between the two countries during the 1950-1953 Korean war, and the current leadership appears reluctant to overrule them. 'At one end of the spectrum, people are suspicions of the US, and are strong supporters of communist countries,' said Nicholas Reader, a China expert at the ICG. 'At the other end, people say Hu Jintao is not pushing enough to make changes, he is not facing down hardliners in the party.' China remains, according to statistics produced by South Korea's central bank, North Korea's top trade partner. Visitors to the nation note that goods traded in markets are almost exclusively of Chinese origin. 'Chinese foreign trade is orchestrated at the provincial or central government level - they promote destinations to specific businesses,' said ICG's Mr Reader. 'In a country as sensitive as North Korea, that kind of investment would not be driven by local government, but by the centre.' Noting that such activity begins with 'small, guerilla enterprises' he said: 'I don't think there is a master plan to make North Korea a Chinese adjunct province, but to keep it stable and see it opening up to more normal trade practices, as that is the only hope for long-term transformation.' The end result may be the same: An over reliance on China, pushing No2 trade partner, South Korea, deep into the background. While South Korean businesses in the North are heavily controlled - the flagship South Korea investments, the tourist zone of Mt Kumgang and the Kaesong Special Industrial Zone are completely isolated from the rest of the country - Chinese businessmen are relatively free to come and go, requiring only special car licence plates. 'The Chinese are making a pre-emptive move,' Mr Moon said. 'The South Koreans can't make that move now.' Even so, in Seoul the official line is that Chinese trade is a plus. 'It is true that Chinese investment is increasing, but South Korean investment is also increasing,' Minister of Commerce Lee Heebeom said last year. 'I don't think we are competing there, and I don't think China could replace [South] Korea there.' But a preponderant Chinese commercial presence could have long-term repercussions. 'North Korea will, left to itself, become an economic province of China - and can do very well,' said a European businessman with experience of the country. 'That is a route it can take, independent of aid. Most investment has a Chinese dimension: They are investing in the usual areas - natural resources, infrastructure.' He said Chinese businessmen had an understanding of operating within a communist system that South Koreans lacked, and also enjoyed a pricing advantage. This may explain why, despite officially downplaying the threat of growing Chinese economic influence, Seoul has been pushing joint economic projects and aid packages with its northern neighbour and refusing to link them to progress in nuclear talks. And with neither Beijing nor Seoul willing to withdraw assistance to the North, Washington hardliners are left with few opportunities to apply pressure, beyond the financial sanctions placed after the US Treasury accused a Macau-based bank of laundering counterfeit US dollars from North Korea.