North Korea launched a long-range rocket on Sunday, violating UN resolutions and doubling down against an international community already struggling to punish Pyongyang for a nuclear test last month.

Pyongyang insists its space programme is purely scientific, but most of the world views its rocket launches as disguised ballistic missile tests aimed at developing a weapons delivery system capable of striking the US mainland.

There was no immediate confirmation that the final stage of the satellite-bearing rocket had successfully achieved orbit, and an unconfirmed report from South Korea's Yonhap news agency suggested the second stage may have malfunctioned.

A US defence official said the launch vehicle "appears to have reached space."

North Korean state television said it would make a special announcement at 0330 GMT.

Condemnation was swift, with the United States calling the launch "destabilising" and provocative, while Japanese Prime Minister Shinzo Abe slammed it as "absolutely intolerable."

In New York, diplomats said the UN Security Council would meet in emergency session later Sunday.

- Tough response urged -

South Korean President Park Geun-Hye said the Council should respond quickly with "strong punitive measures" against what she called a grave challenge to global peace and security.

The rocket, carrying an Earth observation satellite, took off at around 9:00 am Pyongyang time (0030 GMT), according to the South Korean defence ministry which was monitoring the launch site.

Its pre-orbital flight arc was planned to traverse the Yellow Sea and further south to the Philippine Sea, with both South Korea and Japan threatening to shoot it down if it encroached on their territory.

Multiple UN Security Council resolutions proscribe North Korea's development of its ballistic missile programme.

Despite Pyongyang's insistence on a peaceful space mission, its rockets are considered dual-use technology with both civil and military applications.

The United States, along with allies like South Korea and Japan, had warned Pyongyang it would pay a heavy price for pushing ahead with launch, but analysts said the North's timing was carefully calculated to minimise the repercussions.

- Good timing? -

With the international community still struggling to find a united response to the North's January 6 nuclear test, the rocket launch -- while provocative -- is unlikely to substantially up the punitive ante.

"North Korea likely calculates that a launch so soon after the nuclear test will probably only incrementally affect the UN sanctions arising from that test," said Alison Evans a senior analyst at IHS Jane's.

North Korea's chief diplomatic ally, China, has been resisting the US push for tougher sanctions against Pyongyang.

While infuriated by North Korea's refusal to curb its nuclear ambitions, China's overriding concern is avoiding a collapse of the regime in Pyongyang and the possibility of a US-allied unified Korea on its border.

North Korea last launched a long-range rocket in December 2012, placing an Earth observation satellite in orbit.

Western intelligence experts said the satellite had never functioned properly, and argued that this proved the mission's scientific veneer was a sham.

- ICBM challenge -

Despite Pyongyang's bellicose claims to the contrary, the North is still seen as being years away from developing a credible inter-continental ballistic missile (ICBM).

Orbital rocket launches, experts say, are relatively straightforward compared to the challenge of mastering the re-entry technology required to deliver a payload as far away as the United States.

"An ICBM warhead, unlike a satellite, needs to come down as well as go up," said aerospace engineer John Schilling, who has closely followed the North's missile programme.

"North Korea has never demonstrated the ability to build a re-entry vehicle that can survive at even half the speed an ICBM would require," Schilling said.

"If and when they do, what is presently a theoretical threat will become very real and alarming," he added.

It is also unclear how far North Korea has progressed in miniaturising warheads to fit on the tip of an eventual ICBM.

The North said last month's nuclear test was of a miniaturised hydrogen bomb. Most experts dispute the claim, saying the yield was far too low for a full-fledged H-bomb.