Wellington, May 26 NZPA - Prime Minister John Key has joined the United Nations Security Council criticism of North Korea's latest nuclear test, describing the blast as a very disturbing event.

The UN Security Council unanimously condemned North Korea's test, saying it was a "clear violation" of a previous resolution passed in 2006 after Pyongyang's first atomic test.

Further action at the United Nations was expected in coming days in response to North Korea's second nuclear test which drew strong rebuke from around the world.

US President Barack Obama said Pyongyang's nuclear weapon programme was a threat to international peace and security and called for an international response.

The North's neighbour and long-time benefactor, China, said it was "resolutely opposed" to the test.

Mr Key also criticised North Korea saying while it was difficult to understand their motivation, a disturbing pattern of behaviour was emerging.

"It's really running against the global sentiment that I think President Obama is trying to set, where we want to see a world with less nuclear weapons."

Foreign Minister Murray McCully refused to comment on the UN declaration saying he had issued a statement on North Korea yesterday.

North Korea's official KCNA news agency reported a successful underground nuclear test had been conduct on May 25 "as part of the measures to bolster up its nuclear deterrent for self-defence".

It added that the test was "safely conducted on a new higher level in terms of its explosive power and technology of its control."

NZPA