China on Wednesday joined the global chorus of anger and concern over a planned rocket launch by North Korea, as Japan vowed to shoot down any missile that threatened its territory.

UN Secretary-General Ban Ki-moon meanwhile urged the reclusive communist state to scrap its plans for the rocket launch -- another major violation of UN resolutions just weeks after its fourth nuclear test.

Pyongyang on Tuesday confirmed that it would launch a rocket sometime between February 8-25, which is around the time of the birthday on February 16 of late leader Kim Jong-Il, father of current leader Kim Jong-Un.

"We express serious concerns about that," foreign ministry spokesman Lu Kang said in Beijing, calling on Pyongyang to abide by UN strictures forbidding its use of ballistic missile technology.

Ban held talks on the planned rocket launch in London at the International Maritime Organisation, which received a notice from North Korea.

A former South Korean foreign minister, the UN chief said North Korea's announcement was "a deeply troubling development" and offered his help to reduce tensions and facilitate dialogue with Pyongyang.

"It will further aggravate the profound concerns that the international community already has in the wake of the nuclear test," said a statement from his spokesman.

The North insists its space programme is purely scientific in nature, but the United States and its allies say its rocket launches are aimed at developing an inter-continental ballistic missile (ICBM) capable of striking the US mainland.

In South Korea the government echoed US warnings that the North would pay a "heavy price" if it went ahead, and Japanese Prime Minister Shinzo Abe condemned what he called a "serious provocation".

Abe's defence minister issued an order to "destroy" the rocket with surface-to-air missiles if it violated Japanese airspace.

North Korea said the sole objective was to place an Earth observation satellite into orbit, but analysts saw the launch announcement as doubling down against an international community already struggling to agree a united response to Pyongyang's January 6 nuclear test.

- 'Classic move' -

"It's a classic move," said John Delury, an associate professor at Yonsei University in Seoul.

"While waiting for a full response for the nuclear test, you might as well sneak in a rocket launch. The North tends to do these things in pairs," Delury said.

The United States, which has been spearheading a diplomatic drive for harsher and more effective sanctions on Pyongyang, was quick to condemn the plan.

Daniel Russel, the assistant US secretary of state for Asia-Pacific affairs, slammed what he called "yet another egregious violation" of UN resolutions and said it should be met with "tough additional sanctions".

UN sanctions were tightened after North Korea successfully placed a satellite in orbit on a three-stage Unha-3 rocket in December 2012.

A fresh launch poses a dilemma for the international community, which is already divided on how to punish the North for its nuclear test.

North Korea's chief diplomatic ally, China, has been resisting the US push for tougher sanctions, but a rocket launch would bolster calls for Beijing to bring its maverick neighbour into line.

"However, I'm not sure if China will change its position," said Delury.

"The nuclear test is a far bigger deal for Beijing than the rocket launch, so I don't expect any tangible shift in China's perspective, whatever the US says," he added.

While its patience has been stretched to the limit by Pyongyang's refusal to curb its nuclear ambitions, China's overriding concern is a collapse of Kim Jong-Un's regime and the possibility of a US-allied unified Korea on its border.

"We don't want to see any escalation of tension, but if relevant countries insist on doing so, then we are not able to stop them," said foreign ministry spokesman Lu.

US Secretary of State John Kerry had sought to pressure his Chinese counterpart Wang Yi during a visit to Beijing last week.

Although the two sides agreed to mount an "accelerated effort" to try to resolve their differences on a new resolution, Kerry acknowledged they had not agreed on the "parameters of exactly what it would do or say".

Since early 2013, North Korea has been upgrading its Sohae satellite launch complex to handle larger longer-range rockets with heavier payloads, but most experts say Pyongyang is still years from obtaining a credible ICBM capability.

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KERRY GROUP