North Korea fired a long-range rocket Wednesday days before the first anniversary of its former ruler's death, magnifying the threat posed by the nuclear-armed state and provoking outrage from the US.

Regional US allies were also angered and even China expressed concern at the successful launch by its wayward communist ally -- while also calling on all sides to avoid "stoking the flames".

The launch triggered plans for an emergency session of the UN Security Council, which has imposed round after round of sanctions against North Korea over its ballistic missile and nuclear programmes.

North Korea insisted the mission was not a banned intercontinental missile test but was designed to place a scientific satellite in orbit, and said it had achieved all its objectives.

"The satellite has entered the orbit as planned," Pyongyang's Korean Central News Agency (KCNA) said in a statement repeated later in a triumphant special broadcast on state television.

North American Aerospace Defense Command officials said the launch appeared to have successfully put an object in orbit.

Masao Okonogi, a professor of Korean politics at Keio University, said 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.

North Korean leader Kim Jong-Un was believed to be keen that the launch fall close to the first anniversary of the death of his father and former leader Kim Jong-Il on December 17.

KCNA hailed it as a "ground-breaking" event that paid tribute to the late Kim's vision and leadership.

The launch took many observers by surprise, coming after many experts said North Korea appeared to be running into technical problems caused by the bitter winter weather.

A previous launch of the same Unha-3 rocket in April had ended in embarrassing failure, with the carrier exploding shortly after take-off.

Success this time carries profound security implications, marking a major advance in North Korea's ability to mate an intercontinental ballistic missile capability with its nuclear weapons programme.

In October, North Korea had said it already possessed rockets capable of striking the US mainland -- a claim that many analysts at the time dismissed as bluster.

In Washington, National Security Council spokesman Tommy Vietor issued a scathing statement that accused North Korea of once again tearing up the international rulebook.

"North Korea's launch today... is a highly provocative act that threatens regional security, directly violates United Nations Security Council resolutions ... and undermines the global non-proliferation regime," he said.

Unusually China -- North Korea's sole major ally and its biggest trade partner and aid provider -- responded relatively quickly with a statement that pressed the country to abide by UN Security Council resolutions.

But in a commentary, state news agency Xinhua also decried "bellicose rhetoric and gestures" by all concerned, and defended North Korea's right to explore space.

"All parties concerned should stay cool-headed and refrain from stoking the flames so as to prevent the situation from spiralling out of control," it said.

Russia labelled Pyongyang's defiance of UN resolutions as "unacceptable" and warned the launch would have a "negative effect" on regional stability.

North Korea is banned from carrying out missile tests under UN resolutions triggered by Pyongyang's two nuclear tests in 2006 and 2009.

Japan's government said it "cannot tolerate" the "extremely regrettable" launch, and South Korea's government convened an emergency meeting of its National Security Council.

"This is a threat to peace on the Korean peninsula and around the world," Foreign Minister Kim Sung-Hwan said.

The UN Security Council said it would meet Wednesday, with one Western diplomat predicting a "strong response".

Pyongyang put the timing of the launch at 9:49 am (0049 GMT) and said the satellite was deployed in orbit nearly 10 minutes later.

The first and second stages fell in the sea west and southwest of the Korean Peninsula, while the third splashed down 300 kilometres (188 miles) east of the Philippines.

US and South Korean officials said it would take time to fully analyse the entire launch and determine its overall success.

North Korea had originally provided a December 10-22 launch window, but extended that by a week on Monday when a "technical deficiency" was discovered.

While the United States and its allies look to ratchet up pressure at the UN, much will depend on the stance taken by veto-wielding member China.

"China sets the maximum response level in the Security Council when it comes to North Korea," said a senior South Korean government official.