North Korea will shift to collective rule from a strongman dictatorship after last week's death of Kim Jong-il, although his untested young son will be at the head of the ruling coterie, a source with close ties to Pyongyang and Beijing said.

The source said the military, which is trying to develop a nuclear arsenal, has pledged allegiance to the untested Kim Jong-un, who takes over the family dynasty that has ruled North Korea since it was founded after the Second World War.

The source declined to be identified but has correctly predicted events in the past, telling Reuters about the North's first nuclear test in 2006 before it took place.

The comments are the first signal that North Korea is following a course that many analysts have anticipated - it will be governed by a group of people for the first time since it was founded in 1948.

The situation in North Korea appeared stable after the military gave its backing to Kim Jong-un, the source said.

"It's very unlikely," the source said when asked about the possibility of a military coup.

"The military has pledged allegiance to Kim Jong-un."

North Korea's collective leadership will include Kim Jong-un, his uncle and the military, the source said.

Jang Song-thaek, 65, brother-in-law of Kim Jong-il and the younger Kim's uncle, is seen as the power behind the throne along with his wife, Kim Kyong-hui, Kim Jong-il's sister.

So too is Ri Yong-ho, the rising star of the North's military and currently its most senior general.

The younger Kim, who is in his late 20s, has his own supporters, but is not strong enough to consolidate power, analysts said.

"I know he's been able to build a group of supporters around himself who are of his generation," said Koh Yu-hwan, president of the Korean Association of North Korean Studies in Seoul.

He said the coterie was set up by Kim Jong-il before he died.

"The relative calm seen these few days shows it has been effective. If things were not running smoothly, then we'd have seen a longer period of 'rule by mummy', with Kim Jong-il being faked as still being alive," he said.

He said the younger Kim would accept the set-up, for now.

Ralph Cossa, an authority on North Korea and president of the US think tank Pacific Forum Centre for Strategic and International Studies, said it made sense that the ruling group would stick together.

"All have a vested interest in regime survival. I think the regime will remain stable, at least in the near-term," he said.