New Zealand will not be signing the United States' document calling for global action on the war on drugs, Prime Minister Jacinda Ardern says.

Photo: RNZ / Chris Bramwell

Ms Ardern is in New York for the United Nations General Assembly this week, along with about 140 other world leaders.

US President Donald Trump is kicking off his week at the UN by holding an event to promote the US document called the Global Call to Action on the World Drug Problem.

The document requires the countries which sign to develop national action plans to reduce the demand for illicit drugs, cut off supply at their borders and strengthen international cooperation.

US media are reporting that some countries will sign it, not because they agree with it but because they don't want to antagonise Mr Trump.

But Ms Ardern said New Zealand would not be among them.

"No it's not our intention to and there are a number of other countries who haven't either."

Ms Ardern said New Zealand had its own specific challenges around drug use, and it would prefer to take a health approach to the issue.

National leader Simon Bridges said a government led by him would sign up to the US document.

He said Ms Ardern was distancing New Zealand from more than 120 countries - including Australia, the United Kingdom and Canada - who had all signalled their intention to take part.

"The Prime Minister's excuse for not signing up, that the government is taking 'a health approach' isn't good enough. The strategy calls for countries to do more to address addiction and provide more treatment as well as working more closely together to clamp down on manufacturing and supply.

"Taken together, that's how we will deal with the drug problem.

"But by distancing New Zealand from that work the Prime Minister risks making New Zealand an easy target and sending the message that her government is soft on crime and drug dealers."

Mr Bridges said National would support people with drug and alcohol problems, but would also hold those who peddle drugs to account.

Ms Ardern also met with the UN Secretary-General António Guterres on Monday morning.

She said she reiterated New Zealand's support for his plans to reform the United Nations.

"Particularly given that from the very beginning we have always opposed to use of the veto, and continue to oppose it.

"Of course the [Secretary-General] has proposed other mechanisms to try and reduce the use of the veto and we support those."

Ms Ardern has meetings planned tomorrow with the leaders of Ireland, Colombia and Austria.

She will also appear on the The Today Show, an American breakfast TV show with an audience of four million.