Kim Jong-il's regime could be left totally and utterly isolated, writes Clifford Coonan, in Beijing
China and North Korea are brothers in arms, communist comrades, close neighbours linked by culture and history and fellow travellers in defiant isolation from the rest of the world.
But the hairline cracks visible in China's relationship with North Korea over its nuclear ambitions are in danger of turning into a seismic fault-line since Pyongyang tested a nuclear device, seemingly against the wishes of Beijing.
"The nuclear test will undoubtedly exert a negative impact on our relations," said a spokesman for China's foreign ministry, Liu Jianchao, adding that Monday's test was carried out "flagrantly, and in disregard of the international community's shared opposition." Strong words from North Korea's only ally of consequence.
And if their Marxist cousins in Beijing turn on Pyongyang over the nuclear test, Kim Jong-il's Cold War relic will be left utterly alone in the world.
Grain and electricity from China fills the ever-present shortfall in North Korea's food and energy needs - some analysts believe it is the only difference between survival and collapse for the desperately poor country of 23 million. The success or failure of international sanctions depends on whether China agrees to stop giving support to the North Koreans.
When North Korea tested missiles for carrying nuclear warheads earlier this year, China's reaction was irate but cautiously so. This time it has been much more forthright and it certainly looks as if the Chinese are sticking to the international line. .
But there are sound reasons why Beijing will feel reluctant to abandon Pyongyang to the full glare of international disapproval.
It fears the destabilising effects of the collapse of North Korea as it would effectively lead to Korean reunification as some kind of capitalist democracy, with the dreadful prospect of US troops on its borders. Or it could mean thousands of refugees streaming across the border into industrial northeast China.
The government in Beijing is again urging diplomatic efforts to resolve the crisis, saying that this is not the time for punishment, certainly not military action, and calling on the United Nations to use "positive and appropriate measures".
"Taking military action against North Korea would be unimaginable. What we should discuss now is not the negative issue of punishment. Instead, the international community and the United Nations should take positive and appropriate measures that will help the process of denuclearisation on the Korean peninsula," the ministry spokesman said. This reaction also underlines Beijing's desire to appear as an honest broker in the Korean nuclear crisis, part of its efforts to match growing economic power with more diplomatic influence.
As a permanent Security Council member, China has a decisive say over how stern a punishment the international community can mete out.
The North Koreans went a step further yesterday in the face-off with the rest of the world. Unnamed spokesmen stepped up the country's threats against Washington, saying North Korea could launch nuclear missiles unless Washington did something to resolve the nuclear stand-off with Pyongyang.
This is sure to rile the Chinese even more, as does the suggestion that North Korea is attempting to put pressure on China. Mr Kim knows that the international community will be unable to push through sanctions unless China plays ball. Sanctions would include checking on every shipment going into North Korea for signs of nuclear equipment, or cracking down on Mr Kim's notorious business empire, known as "Division 39", a murky labyrinth of accounts in Macau and Switzerland rumoured to contain billions of dollars.
What China does not want is to become isolated internationally over the Korean nuclear stand-off. Chinese economic growth in the last 20 years has been largely underwritten by trade with the US and Europe, and it cannot risk becoming an economic pariah alongside its geographical and ideological neighbours in Pyongyang.