The nuclear test announced by North Korea is unpardonable and irrational, New Zealand Foreign Minister Winston Peters said on Monday.
"If Pyongyang's claims are true, they have acted in an irrational way that ignores the clear advice of the United Nations Security Council and international community," Peters said.
"Such action is unpardonable and inconsistent with the behaviour expected of a state seeking security and other guarantees from the global community."
A nuclear test would be viewed by many as having "crossed the red line and represents an extreme escalation of North Korea's previous unacceptable behaviour", he said.
He said the test changed the security environment for China, Japan and South Korea.
Peters added that "this is a time for cool heads and we urge all parties to refrain from acts which may add to a further deterioration of the situation".