Foreign Affairs Minister Nanaia Mahuta has recognised and congratulated President-elect Joe Biden and Vice President-elect Kamala Harris, noting Biden's previous visit to New Zealand.

And she paid special tribute to Harris, who she said will bring "some very unique attributes to their leadership" as the first woman-of-colour Vice-President.

Mahuta, who was sworn in as Foreign Affairs Minister on Friday, addressed media this morning following Prime Minister Jacinda Ardern's message of congratulations to Biden.

She said New Zealand had warm relations with Biden when he was Vice President to Barack Obama.

"He visited here in 2016, met a number of people and by all accounts enjoyed himself.

"I anticipate that there will be continued warm conversations on areas of common interest like Covid-19, like trade, like this issue of global economic recovery.

"We enjoy our relationship with them. We want to continue to strengthen that relationship, and under a new regime there is opportunity for greater cooperation."

She wouldn't be drawn on Trump's reaction or whether he might refuse to physically leave the White House.

Trump's legal action was a matter for the US, she said.

Asked if Trump's behaviour was becoming of an outgoing president, Mahuta said: "It's for American voters, really, to decide that level of behaviour but they have made their decision known through the election."

Asked about the US joining the Trans-Pacific Partnership and rejoining the Paris climate agreement, Mahuta New Zealand would prioritise which issues to discuss once Biden got his feet under the table in January next year and his agenda became clearer.

"My area of priority today is to congratulate President-elect Biden and to acknowledge Kamala Harris ... it's an exciting time for them."

Ardern said this morning the relationship between New Zealand and the US is strong.

"I look forward to developing even closer relations with the incoming Biden Administration," she said.

"As Vice President, Joe Biden was a close friend of New Zealand and visited here in 2016, the most senior US politician to do so since President Bill Clinton attended APEC in 1999.

"New Zealand will continue to work side-by-side with the United States on the issues that matter to both of us, including the prosperity, security, and sustainability in the Indo-Pacific and Pacific Island regions.

"The campaign by the President-elect has also shown the shared interests we have in addressing global challenges like Covid-19 and climate change.

"There are many challenges in front of the international community right now, the message of unity from Joe Biden positions us well to take those challenges on."

She also acknowledged outgoing President Donald Trump.

"New Zealand has enjoyed positive and cooperative relations with the United States over the period of the Trump Administration, especially in the Indo-Pacific and Pacific Island regions," Ardern said.

Biden is set to become the 46th President of the United States, after he passed the 270 Electoral College votes needed with a win in Pennsylvania early this morning (NZ time).

He said in a statement he was "honoured and humbled".

"It's time for America to unite. And to heal," he said. "We are the United States of America. And there is nothing we can't do, if we do it together."

After TV networks called the race for Biden, Trump said in a statement that Biden was "rushing to falsely pose as the winner" and said it was "far from over".

"Beginning Monday, our campaign will start prosecuting our case in court to ensure election laws are fully upheld and the rightful winner is seated."

"I will not rest until the American People have the honest vote count they deserve and that Democracy demands," Trump said in the statement.

Mahuta is expected to talk about what a Biden presidency will mean for New Zealand.

Ardern has previously spoken about the importance of a rules-based multilateralism, in stark contrast to Trump's doctrine of protectionism and America First.

Ardern has joined British Prime Minister Boris Johnson, French President Emmanuel Macron, Canadian Prime Minister Justin Trudeau and other world leaders in offering her congratulations.