In a meeting late yesterday with President Xi Jinping of China, Mr Key acknowledged Beijing's leadership role in trying to reinforce a peaceful way through the threats of war by North Korean leader Kim Jong Un.
After the meeting, Mr Key said the gravity of the North Korean issue was not lost on Mr Xi.
"His words were they are totally committed to peace on the Korean Peninsula."
Green Part co-leader Dr Russel Norman said Mr Key had "totally jumped the gun" with his comments about potential conflict in Korea.
"What we need to do is breathe through our nose and try to calm the situation down. The last thing we need is the Prime Minister of New Zealand going to China and talking about a war on the Korean peninsula.
"It seems to me international law and working within the UN charter should be the framework for the New Zealand Government's response, not as John John Key says where the US and Australia goes, New Zealand goes," he told RNZ.
Labour leader David Shearer said the Prime Minister's comment's were irresponsible.
"The focus should be on de-escalation rather than ramping up the rhetoric.
"The clear implications of John Key's comments were that we should automatically follow the United States and Australia into a war in Korea. No one should be talking up the prospect of war on the Korean Peninsula. In fact, the international community is focused on de-escalation and so should we."
Mr Shearer said New Zealand needed to work within a multilateral framework.
Labour's foreign affairs spokesman Phil Goff said North Korea's rhetoric represented "dangerous brinkmanship" and should be condemned.
"John Key's response was amateurish and ill-timed.
"He got talked into a response that was ill-judged, it is similar to his knee-jerk reaction at the time of the invasion of Iraq.
"New Zealand does not blindly follow any other country with respect to decisions about engaging in wars," said Mr Goff.
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