New Zealand has reaffirmed its support for Ukraine following the Oval Office clash between Ukrainian President Volodymyr Zelensky and US President Donald Trump.

The meeting devolved into a shouting match before Zelensky left.

In a statement on Sunday afternoon, Prime Minister Christopher Luxon said he was aware of the "robust exchange".

"New Zealand remains steadfast in its support for Ukraine as it defends itself in a war that Russia started. It's mounting the defence of a proud, democratic, sovereign nation, but also the defence of international law.

"The best route to peace is for Russia to cease its three-year long illegal and immoral war of aggression. We all want the US and Ukraine working together towards the shared objective of a just and lasting peace for Ukraine," Luxon said.

Earlier in the day, Labour leader Chris Hipkins said the meeting between Trump and Zelensky showed things were "volatile" at the moment.

"I really felt for Zelensky, President Zelensky, I've met him, I think he's actually a very patient man, he's a very resolved man, and I have huge sympathy for the situation that he finds himself in.

"I think he's led Ukraine with exceptional leadership over the last couple of years and I think the world community should continue to support Ukraine."

Hipkins said he didn't believe Zelensky was being disrespectful.

New Zealand should remain committed to an international system of rules and what was happening in Ukraine was not consistent with those rules, Hipkins told reporters at Te Matatini.

"I certainly think it would be appropriate for New Zealand to continue to express it's support for Ukraine, for us to continue to urge other countries to support Ukraine as well... through all of the international relationships that we have we should be continuing to encourage other bigger global partners to do the right thing."