Australia on Monday said it was critical governments exercised calm and restraint after the death of North Korean leader Kim Jong-Il, while urging Pyongyang to engage with the global community.

The North's state media, in a shock announcement, reported Monday that the 69-year-old Kim died of a heart attack Saturday while on board a train during one of his field trips.

Australian Foreign Minister Kevin Rudd said nuclear North Korea was the single most armed military zone anywhere in the world and it was at a critical juncture.

"Two critical points need to be emphasised at this important time," he said.

"The first is that all governments, including the government of North Korea, should at this time be exercising maximum calm and restraint both in terms of what they do and in their diplomatic signalling.

"It is at times like this that we cannot afford to have any wrong or ambiguous signalling.

"This time also presents an important opportunity to the new North Korean leadership to engage fully with the international community on how to improve their economy in order to properly feed their people and critically on how to deal with the outstanding problem of North Korea's nuclear weapons programme."

Rudd said Canberra would remain in close contact with allies the region in the days and weeks ahead, with the leadership transition "uncertain".

"The political succession in North Korea is uncertain," he said.

"It will be difficult to read in the immediate days ahead precisely what will transpire in terms of the future of the North Korean leadership."

Kim's youngest son Kim Jong-Un, who Rudd said was 28, is seen as the heir apparent. (AFP)