North Korea launched a long-range rocket Wednesday days before its young ruler marks 12 months in power, intensifying the threat posed by the nuclear-armed state and provoking global condemnation.

The United States and its allies were infuriated and even China expressed "regret" 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, to little avail.

North Korea insisted the mission was not a banned inter-continental 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.

The US military said the launch appeared to have successfully put an object in orbit.

Masao Okonogi, a professor of Korean politics at Keio University in Japan, said the launch would thrust North Korea close to the top of Washington's national security agenda as President Barack Obama prepares for a second term.

"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," he said.

Defying the international uproar, the North vowed more launches.

"No matter what others say, we will continue to exercise our legitimate right to launch satellites," said a foreign ministry spokesman, urging the international community to stay cool "to prevent the situation from developing (in an) undesirable direction".

The country's leader Kim Jong-Un, who is in his late 20s, 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, and described "enormous joy" and tears of elation from ordinary people.

Others such as the government of Britain said the isolated state, which has suffered intermittent famines in the past two decades, would have been better off spending its meagre resources on its own people.

The launch took many experts by surprise, coming after they had 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 Washington, National Security Council spokesman Tommy Vietor 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 in a statement.

North Korea denies US accusations that, down the years, it has exported its nuclear technology to Pakistan and missile expertise to Iran.

Unusually China -- North Korea's sole major ally and its biggest trade partner and aid provider -- responded relatively quickly by expressing "regret" and pressing the country to abide by UN 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.

Russia labelled Pyongyang's defiance of UN resolutions "unacceptable" and warned the launch would have a "negative effect" on regional stability, while the European Union threatened new sanctions.

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

Japan's government said it "cannot tolerate" the launch, and South Korea's government convened an emergency meeting of its National Security Council, describing its northern rival as a menace to peace.

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.

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.