Jacinda Ardern says rumours she's not well enough to be Prime Minister are "disappointing" and not true.

Taking questions on RadioLIVE on Friday, host Mark Sainsbury asked the Labour leader if she knew about the rumours.

"People are putting out stories about you... [that] your health is not up to the job, that you've been hospitalised," Sainsbury said.

"In other words, 'Keep away from her, she is not up to it.' Are you aware of that?"

Ms Ardern said she was aware of rumours, and was happy to "correct the record".

"I think that's reflecting a time when I had an unfortunate complication with tonsillitis - something called quinsy," she explained.

"That was the basis on which that started. New Zealand, in different forms, gets plagued by gossip and hearsay, and I am happy to bat back on things like that. But ultimately what I hope is people will see me for who I am - that I'm upfront, that I address problems as they arise, that I'm someone who has enough courage to be in politics in the first place, let alone taking on this job under these exceptional circumstances.

"I am robust enough for this job."

As far as she knows, the rumours weren't started by her political opponents in Parliament. Even if they were, she wouldn't retaliate in kind - nor would she play the 'good cop' while someone else plays the bad.

"Straight bat for us. We've got to win on our own merits."

Those merits, she acknowledged, include the so-called 'Ardern effect' that's seen the 37-year-old revive the party after nearly a decade of decline in the polls.

A new poll Friday morning had 32 percent of voters rating her the most capable of leading Parliament. That's well behind National's Bill English on 45 percent, but a vast improvement on her predecessor Andrew Little, who only managed 10 percent in a previous version of the same poll.

"I looked at it and thought, that's not bad. Bit of room for improvement there, but that's not a bad start," she told Sainsbury.

'Jacindamania', or 'Jacindageddon'?

Sceptics have wondered why voters are flocking to Labour under Ms Ardern, when the party's offering largely the same policies as it did under Mr Little. Opportunities Party leader Gareth Morgan controversially wondered if she'd be more than "lipstick on a pig" - the pig being Labour.

Ms Ardern says voters tend to have a 50-50 split in how they decide who to vote for - half personality, half policy.

"It's 50 percent, 'I want to know who this person is because I need to trust their judgement, because they're going to make calls on issues that aren't there for me to think about when I cast my vote now.' So knowing us matters.

"The other 50 percent is, 'Where are you going to take me? What are your ideas? Do I agree with your vision and your values and the plan that you have for New Zealand.'

"So I get the first part - I get why it matters."

She laughed off suggestions the country was gripped in 'Jacindamania'.

"Some people call it Jacindageddon - not everyone's positive."

Newshub.