Dozens of countries, including New Zealand, have signed a treaty to ban nuclear weapons amid tensions over North Korea's nuclear and missile tests.
The US, Britain, France and others, including Australia, boycotted the event at the annual United Nations gathering of world leaders.
The treaty on the prohibition of nuclear weapons will enter into force 90 days after 50 countries have ratified it. Only a few states were due to deposit their ratification on Wednesday.
"There remain some 15,000 nuclear weapons in existence. We cannot allow these doomsday weapons to endanger our world and our children's future," UN Secretary-General Antonio Guterres said as he opened the treaty for signing.
Foreign Minister Gerry Brownlee called the treaty " consistent with New Zealand's long-standing commitment to international nuclear disarmament efforts".
"While no state currently in possession of nuclear weapons will be signing along with us, this treaty nevertheless represents an important step towards a nuclear-free world," he said earlier this week.
Earlier this month North Korea conducted its sixth and largest nuclear weapons test. American President Donald Trump told the 193-member UN General Assembly on Tuesday that if threatened, the US would "totally destroy" the country of 26 million people and mocked its leader, Kim Jong-un, as a "rocket man".
The treaty was adopted in July by two-thirds of the 193 UN member states after months of talks, which the US, Britain, France and others skipped. They instead pledged commitment to a decades-old Non-Proliferation Treaty, which aims to prevent the spread of nuclear weapons and weapons technology.
The US, Britain and France are among nine countries believed to have nuclear weapons.
Concern over Trump's comments
Russia says it is "extremely concerned" by US President Donald Trump's comments questioning the Iran nuclear deal and suspects that Washington itself may have violated a landmark arms control treaty, Foreign Minister Sergei Lavrov says.
Mr Lavrov's comments, made to Russian reporters at the United Nations in New York, illustrate how deeply Moscow and Washington are at odds over an array of issues and suggest any attempts to improve already battered relations face an uphill struggle.
Addressing the United Nations General Assembly on Tuesday, Mr Trump said Iran's 2015 pact with six world powers to curb its nuclear program in return for loosening economic sanctions was "an embarrassment to the United States". Washington could not abide by an agreement "if it provides cover for the eventual construction of a nuclear program", Mr Trump said.
Mr Lavrov, whose country is a signatory to the deal, said Russia strongly disagreed with that stance.
"It's extremely worrying," he said. "We will defend this document, this consensus, which was met with relief by the entire international community and genuinely strengthened both regional and international security."
Mr Trump's threat in the same UN appearance to "totally destroy" North Korea if it had to defend itself or it allies also went down badly with Russia, which shares a border with North Korea and believes negotiations and diplomacy are the only way to resolve a crisis over Pyongyang's missile program.
"If you simply condemn and threaten, then we're going to antagonise countries over whom we want to exert influence," said Mr Lavrov, referring to Trump's comments.
He saved some of his harshest criticism however for what he said was a possible violation by the US of a landmark 1987 arms control treaty which bans Russian and American intermediate-range missiles on land.
A senior Trump administration official accused Russia earlier this year of violating the same pact, the Intermediate-range Nuclear Forces treaty, something Moscow denied.
But Mr Lavrov said it looked like it was Washington, which is in the midst of a US$1 trillion, 30-year modernisation of its aging ballistic missile submarines, bombers and land-based missiles, that was in breach of the same treaty.
"We have suspicions on at least three fronts that the Americans are creating weapons systems which violate or could violate the treaty obligations," said Mr Lavrov, who said Moscow had relayed its concerns to the US.
Reuters / Newshub.