Prime Minister Jacinda Ardern has passed on "New Zealand's best wishes" to Covid-19 infected US President Donald Trump and his wife, Melenia.

"We have seen now several world leaders who are being affected by Covid-19 and I know that I stand with others in wishing all the best," she told reporters this afternoon.

"This is, obviously, a virus that has had a devastating impact."

She has asked her officials at the New Zealand Embassy in the US to pass along a message, wishing "the President a speedy recovery on behalf of New Zealand".

When UK Prime Minister Boris Johnson had Covid-19, Ardern sent him a text wishing him the best.

Asked if she had done the same for Trump, she said she had not as she does not have his personal phone number.

"Instead, we have used our official channels to pass on that message."

She plans to convey that sentiment in person, when she gets a chance to.

Ardern said that New Zealand would wish anyone experiencing Covid-19 a speedy recovery – "and our very best wishes".

She said it was too early to say what the implication of Trump's diagnosis was for New Zealand.

"We still haven't seen out of the administration the likely effect they believe it will have on the election campaign."

She noted that there has never been a time in US history that an election date has been moved.

"At this stage, I would say it would all be highly speculative – we just haven't had anything official from the White House in that regard."