A historic breakthrough has been made in New York with the adoption of the Treaty for the Prohibition of Nuclear Weapons.

More than 120 countries have agreed they'll never develop, test, acquire or stockpile nuclear weapons, but not one of the countries which already has them is involved.

The Green Party's Disarmament Spokesperson Kennedy Graham said those countries don't want to be forced into signing away their so-called "power".

Mr Graham said even so, the Treaty is arguably the UN's biggest achievement ever.

"You've got 15,000 nuclear weapons, 1800 on high alert - still to this day - increasingly social and political chaos [and] instability," he said.

"The only way to solve all of this is to engage in peaceful negotiation, back off your military exercises, engage in dialogue, reduce the tension and strengthen the international legal norms."

The odd one out on the Treaty is the Netherlands, which doesn't have nuclear weapons of its own but does host American weapons on its territory.

The next step is for countries to actually sign the treaty, once 50 nations have done so it's considered to be ratified.

Peace activists say New Zealand played a key role in building support for the treaty.

New Zealand was a Vice President of the UN conference and the Ministry of Foreign Affairs and Trade worked over the past five years on the initiative to ban nuclear weapons.

Peace Movement Aotearoa says its potential to end the threat of nuclear destruction is a gift for future generations.

However, Foreign Affairs Minister Gerry Brownlee said we need to be realistic about the prospects of this treaty leading to a reduction in nuclear weapons in the short term.

But he said the treaty is an important step towards a world free of nuclear weapons.