The Kiwi leader is in America on an official visit, and on Thursday (Friday AEST) had the honour of delivering Harvard University's Commencement Address.

Ms Ardern had been unable to confirm a meeting with US President Joe Biden, with her office citing Ms Ardern's recent bout of COVID-19 as a complicating factor.

But the leaders will now catch up face-to-face on Tuesday local time, when Ms Ardern will also meet Vice President Kamala Harris.

"It's incredibly important for New Zealand," Ms Ardern said.

"Making sure we have strong relationships with the likes of the United States, while we have the war in Ukraine and increasing tension in our region, is important."

It is the first trip to the White House for a New Zealand leader since Sir John Key met Barack Obama in 2014, though Ms Ardern held a brief meeting with Donald Trump in 2019 at the United Nations.

The prime minister said she would use the visit to champion free trade talks, while Russia's invasion of Ukraine and the geopolitical battle for the Pacific being waged between the US and China will also be on the agenda.

Ms Ardern's visit has coincided with the deadly school shooting in Texas that has left 21 dead, leading to her speaking of New Zealand's gun law reform in the wake of the 2019 Christchurch mosques terror attack.

She said she was not going to preach to Mr Biden on the merits of banning semi-automatic weapons in what she saw as a domestic matter for the US.

"I will certainly, though, be passing on New Zealand's sorrow for what we have seen. To see children at the heart of this most recent event is devastating," she said.

Australian Associated Press