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While Western leaders and editorials have condemned North Korea's artillery barrage of its southern neighbour on Tuesday, in China the response has been more muted.

The authorities expressed concern over the incident and called for both countries "to do more" to contribute towards peace.

But Beijing did not condemn North Korea's actions.

Apart from issuing a couple of bland statements, the authorities here have said nothing.

That is not surprising.

When it comes to North Korea, Beijing almost never criticises its neighbour, no matter how troublesome it proves.

The state-run media has followed suit.

It has not pointed the finger at Pyongyang and gave play to North Korean claims that the border exchange was triggered by South Korea.

One newspaper editorial even praised Pyongyang for showing what it called "toughness" during the skirmish.

Beijing, however, finds itself in a difficult position.

It is North Korea's main ally, supplying much of the country's food and fuel.

It is also a relationship that was forged during the Korean War and has now lasted more than half a century.

When the reclusive North Korean leader, Kim Jong-il, needs foreign backing, he boards his train and heads to China.

He has been in the country twice this year.

Once after the sinking of a South Korean warship, which a team of international investigators said was caused by a North Korean torpedo.

And then ahead of a major military parade in which his son, Kim Jong-un, was unveiled as his likely successor.

Beijing views the country as a buffer state against a democratic South Korea and American forces stationed there.

And if the North Korean regime were to collapse, hundreds of thousands, perhaps millions of refugees would cross the border.

In recent years, however, the relationship between the two countries has been strained.

After North Korea detonated a nuclear device for the first time in 2006, Beijing voted to impose UN sanctions on the country.

It was a rare moment when China sought to publicly punish the regime.

With China now a world power some Chinese see their country's continued support of North Korea as something of an embarrassment.

Indeed, the West hopes that Beijing can exert its influence in Pyongyang to ease tensions.

But for all the help the authorities here give their neighbour, it is unclear how much leverage China actually has over North Korea.

While in public the Chinese authorities will not be criticising North Korea, in private, there will be deep concerns in Beijing that Pyongyang's actions could threaten regional stability.

This latest attack may strengthen those in Beijing who view the country as more of a liability than an asset.