Labour's foreign affairs spokesman David Shearer says there is a chance Iran and South Korea could arm themselves with nuclear weapons under a Donald Trump presidency.
The Republican candidate won the US presidential race in an unexpected landslide victory.
Mr Shearer told Paul Henry there will be global uncertainty because no one knows which of Mr Trump's policies will come into force.
"I think everybody will be concerned about the instability and the vacuum of what the Trump presidency is going to mean."
The former United Nations worker said if Mr Trump renegotiates the Iranian nuclear deal, as he promised to on the campaign, it is a real concern.
"If that happens then you have a nuclearised Iran. That creates a whole new ballgame in the Middle East."
Mr Trump also talked about pulling resources out of Asia, which could have consequences equally as catastrophic.
"Telling the Asian countries - Japan, Korea - they are going to have to look after themselves may mean that in the face of a nuclear North Korea, may mean that South Korea becomes nuclearised."
However Mr Shearer says if the President-elect chooses the right advisors, the crisis could be averted.
"The biggest and most important issue is going to be who he chooses as Secretary of State, and who he chooses to be as his representative in New York at the United Nations."
Mr Shearer says many claims were made on the campaign trail, but it is now time for Mr Trump's aides to write some considered policies.
"The people who he surrounds himself with will make the biggest difference in where Trump is going because I think his ideas, from what I've heard are pretty unformed - he says things on election campaigns, but he hasn't perhaps thought those through in terms of the implications globally."
Mr Shearer also highlights the Ukraine as the biggest loser of the election.
"In the sense that if the United States pulls back from NATO... it gives Russia a greater degree of being able to dominate in that eastern part of Europe. So there is some real anxiety in those border states about what this is going to mean."