North Korea's rocket launch is evidence of a new ballistic missile capability that sharply raises the stakes over Pyongyang's nuclear programme and poses a direct threat to the United States, analysts say.

Although the isolated state faces a stiff technical challenge in shaping, fitting and accurately delivering a long-distance nuclear payload, Wednesday's launch marks a major upgrade of its potential strategic military ability.

"This launch certainly bolsters their credibility when they say that they have missiles that can strike the United States," said James Schoff, a senior associate at the Carnegie Endowment for International Peace.

"It's harder to wave that off after a successful test like this," said Schoff, a former Pentagon official.

A North Korean claim in October that it already possessed rockets capable of striking the US mainland had been widely dismissed as rhetorical bluster at the time.

Masao Okonogi, a professor of Korean politics at Keio University, agreed that the launch would thrust North Korea close to the top of Washington's national security agenda.

"Putting a satellite into orbit means that you have technology to get a warhead to a targeted area. Now, North Korea is becoming not only a threat to the neighbouring countries but also a real threat to the United States," Okonogi said.

"The question is whether the satellite was precisely put into the planned orbit or veered away."

US and South Korean officials said it would take time to fully analyse Wednesday's launch, which Pyongyang described as a purely scientific space mission, but its critics condemned as a disguised ballistic missile test.

Even if the North has achieved its stated objective of placing a satellite in orbit, several analysts cautioned against over-stating its new military capabilities.

Miniaturising a nuclear weapon into a warhead that would fit on a ballistic missile is an enormous technical challenge, and there are still significant questions over accurate delivery, they said.

"It's one thing to have a missile with sufficient range to reach Hawaii. It's another to have sufficient accuracy to hit what you're aiming at," said Ralph Cossa, president of the Hawaii-based Pacific Forum of the Center for Strategic and International Studies.

"It means they have a pretty good chance of hitting the Pacific Ocean but not much chance hitting an island, much less a specific target," said Cossa, a former US Air Force colonel.

"Nonetheless, they are getting better and we have to take them seriously."

Pyongyang's nuclear programme remains shrouded in secrecy, but the country's existing plutonium stockpile is estimated to be enough for six to eight atomic bombs.

Ham Hyeong-Pil, from the South Korea Institute for Defense Analyses, said Pyongyang would move quickly to refine the missile's accuracy and perfect warhead miniaturisation techniques.

"I personally believe that it won't take long for the North to master these two technologies, once it overcomes some technical problems and stages two or three more launches down the road," Ham said.

"It's a worrying situation. I think that the US has no choice but to recognise it as a real, tangible threat," he added.

The timing of Wednesday's launch was widely seen as politically motivated, with the North's leader Kim Jung-Un determined that it should take place close to the first anniversary of the death of his father and former leader, Kim Jong-Il on December 17.

"Kim Jong-Un gains a lot from this in terms of his securing his position and prestige," said Yang Moo-Jin, a professor at the University of North Korean Studies in Seoul.

A previous launch attempt in April, for which Pyongyang had taken the unprecedented step of inviting the foreign media, ended in an embarrassing failure when the carrier exploded shortly after take-off.

The UN Security Council was due to meet later Wednesday to discuss its response to the launch, with the US and its allies demanding a significant expansion of sanctions already imposed after the North's nuclear tests in 2006 and 2009.

Much will depend on the stance of veto-wielding China -- Pyongyang's only major ally and main aid donor -- which has resisted the call for tougher sanctions in the past.

China expressed concern at Wednesday's launch and called on all sides to avoid "stoking the flames".

Cossa said Pyongyang's action would present a key challenge to Chinese leader-in-waiting Xi Jinping, who will formally become president in March.

"Most Chinese say Xi is already calling the shots so this becomes his first test on how he deals with an international crisis," Cossa said.

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