Despite international condemnation of North Korea's artillery attack on the South Korean island of Yeonpyeong in November, which left two marines and two civilians dead, China has remained conspicuously neutral on the issue. China's role as North Korea's only true remaining ally is nevertheless an increasing source of embarrassment to it. Although the Chinese authorities have expressed concern over the latest incident, they have refused to condemn North Korea, instead calling for both the North and the South to do more to ensure peace on the Korean peninsula. China's unwillingness to blame North Korea publicly for the attack (following a similar refusal to hold the North responsible for sinking a South Korean frigate, the Cheonan, in March) comes despite growing international pressure.

Many in the international community would like China to do more to bring its ally to heel, especially given the leverage that it enjoys as North Korea's largest aid provider and main trading partner. The Chinese authorities have many reasons to be concerned about North Korea's recent behaviour. China's efforts to portray itself as a responsible global power are suffering owing to its provision of economic aid and diplomatic support to a rogue state. In addition, there are fears in government circles that North Korean brinkmanship could overshadow the visit of the Chinese president, Hu Jintao, to the US in January 2011. Moreover, China's support for the North Korean regime is getting in the way of a burgeoning economic relationship with South Korea. China did not establish formal economic ties with the South until 1991, but the value of its bilateral trade with South Korea reached US$156bn in 2009, compared with just US$2.7bn with North Korea.

There are, however, a number of reasons why there is unlikely to be a sudden reversal in China's stance towards its long-time ally. Despite three decades of economic reform and modernisation in China that has opened the country up to the rest of the world, Chinese ties with North Korea remain close. The two countries fought together during the Korean war, prompting China's then leader, Mao Zedong, to declare that China and North Korea were as close as "lips and teeth". Military ties are especially close, and the influence of the Chinese People's Liberation Army has been crucial in ensuring continued political support for North Korea from China, despite the diplomatic trouble that it causes.

China is also worried about the potential implications of regime change in the North, the most likely outcome of which would be the reunification of the two Koreas-a scenario that the Chinese government is thought not to be keen on. It regards North Korea as a valuable bulwark between itself and South Korea, largely because of the thousands of US troops that are stationed in the South. Chinese military planners would regard the possibility of a US military presence on their doorstep with horror. In addition to these fears, the authorities are concerned that a sudden implosion of the North Korean government could lead to a destabilising flood of refugees across the border into north-eastern China. According to some estimates, up to 300,000 refugees have already crossed the border from North Korea into China. The collapse of the regime would lead to an estimated 3m more people fleeing North Korea, and many of them would head to China.