An appeal to the two Sudans – which seem to be in danger of slipping into war – for a return to the negotiating table was unexceptional other than that it came from Chinese President Hu Jintao.

"The urgent task is to actively cooperate with the mediation efforts of the international community and halt armed conflict in the border areas," he said.

The simmering conflict between Sudan and South Sudan has delivered a moment that's been coming since China began to escalate its presence in Africa: the collision of Beijing's commercial interests with its policy of non-intervention.

In the civil war years which laid waste to much of southern Sudan, Beijing was the comic book villain. Any attempts to use the UN Security Council to act against the Sudanese regime were blocked by Beijing.

The complaints about China in Africa played out in its defence of Khartoum, as it armed and shielded a hardline regime guilty of war crimes against its own population.

While critics followed the flow of oil from Port Sudan to the country's biggest buyer China, Beijing wheeled out its pat answer that it had no right to intervene in the internal affairs of another nation.

Now, the divorce of the Sudans and its acrimonious aftermath has divided that oil between two countries, which both see China as an ally.

Two-thirds of Sudan's crude reserves are south of the disputed border and while the extraction infrastructure points north, it's already clear that China expects to be the main investor in new pipelines to change that reality.

As a result it has been forced into a role more typically played by Washington, and its stance has been similar.

South Sudan's President Salva Kiir, state visit, to Beijing this week, will remind northern leader Omar al-Bashir of how times have changed. He can no longer count on support in return for cheap oil.

Beijing is in a unique position to affect the outcome of this crisis as it has greater leverage over both sides than the US, which has invested hugely in peace in Sudan, with mixed results.

For many China watchers and some of Beijing's diplomats this was always the intended outcome of the great opening towards Africa. The continent with its natural resources and need for investment have made it an ideal theatre for Chinese diplomacy to define itself.

There are constraints on Khartoum and Juba's capacity to wage war, with both relying to some extent on the sale of oil futures contracts. It's hard to see that either can afford to ignore Beijing. A peaceful outcome could set a profoundly important precedent for China's role in world affairs.