Sydney Morning Herald: China asked its military to study a quick intervention in North Korea but decided that its relationship with the United States was more important than propping up the Stalinist state, with which it shares a border.

A source in Beijing said the study for a pre-emptive Chinese invasion was ordered by a Chinese Communist Party working group formed in late February under the country's senior leader, Hu Jintao.

The result of the study was negative. The People's Liberation Army concluded that although the Chinese-North Korean border was only lightly defended, the Chinese lacked the logistical capability of racing to the demilitarised zone facing South Korea.

"That this kind of thing is being considered in China tells us about the gravity with which this is being regarded in Beijing," said a senior Western diplomat closely following the crisis.