Jane Macartney, Beijing Correspondent of The Times explains why China is now in a Catch-22 situation after North Korea's test of a nuclear bomb.

Beijing's language today shows a high level of disapproval of Pyongyang and is really unusually harsh given China's reluctance to criticise, at least openly, one of its oldest and closest friends.

However, it is true that relations are no longer at the peak that we saw when Kim Il Sung was still in charge. China was nervous about the ascent of his son, Kim Jong Il. While they have nurtured the relationship, there is more distance and, I suspect, more suspicion even than they felt towards his father.

But there is no doubt that China is really North Korea's closest friend, the last real communist cousin, if you like, that this isolated Stalinist state still has.

This makes the situation tricky for China. It doesn't want to antagonise an old friend but nor does it want to see a nuclear power literally on its border. That brings all sorts of factors that could fuel instability in the North Asian region.

China faces a huge dilemma. Do they go beyond words? Do they consider sanctions? What course of action can they take that will enable them to maintain their image as a mature member of the international community while ensuring they do not destabilise North Korea?

The Chinese will be very reluctant to impose sanctions. They may choose to use the lever of aid. China provides almost all North Korea's energy needs and is also a major supplier of food. They could perhaps reduce, or even, halt energy exports. They did that once before under the guise of pipeline maintenance and Pyongyang returned quickly to the negotiating table.

But there's a risk there too. North Korea could feel that it is losing its only real friend and sense that it is being backed even further into a corner. For China, its policy of negotiations rather than pressure doesn't seem to have worked with North Korea, but Pyongyang's reclusive leader could respond with greater extremes of behaviour if they felt even more cornered.

Beijing wants to maintain a balance. It fears that cutting off aid to North Korea could destabilise a neighbour. The risk there is the potential collapse of North Korea since that could lead to a flood of refugees into China. That is the last thing that China wants.

It is keen to retain the status quo in North Korea for several reasons.. It wants to help a fellow communist government, it does not want instability on its borders and it likes to have a buffer between the Chinese frontier and South Korea where so many thousands of American troops are stationed.

The instability could spread further. If North Korea goes nuclear then both Japan and Taiwan could decide to activate nuclear programmes. This is a development that China is extremely eager to avoid since this would greatly raise the level of armament in North Asia.

In the case of Japan, China has always had a deep emotional reaction to to any hint that Japan is contemplating expanding its military budget or boosting its defence capabilities. This is not only a strategic consideration but also one most clearly based in history.

So China is in a very difficult position - possibly the most difficult of any country involved in the North Korea nuclear crisis.

I'm not sure they will be able to respond quickly. They will want time to think about their actions and to speak to North Korea about what they are going to do next. They are going to want to try to find out much more about North Korea has achieved with this test and its plans.

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