Prime Minister Jacinda Ardern sees preparations for talks between Donald Trump and North Korea leader Kim Jong-un as a welcome "de-escalation" in their nuclear stand-off.

The May meeting would be the first-ever US-North Korea summit.

President Kim committed to "denuclearisation" and to suspending nuclear or missile tests, South Korea's National Security Office head Chung Eui-yong earlier told reporters at the White House.

White House spokeswoman Sarah Sanders said Mr Trump "will accept the invitation to meet with Kim Jong-un at a place and time to be determined".

Mr Trump tweeted later: "Great progress being made but sanctions will remain until an agreement is reached."

Ms Ardern said talks were something the New Zealand government had been hoping for and she thought it was "a sign we are moving further away" from the prospect of war.

"Open dialogue is something we've wanted to see as opposed to a further escalation - and you cannot get higher level than this," she said.

She said sanctions had been having an impact on North Korea, but that she wasn't sure if the meeting would lead to a long-term solution to the stand-off.