Whether the three-way race for National becomes a four- or even five-way tussle is expected to be known on Monday.
Contenders Amy Adams, Simon Bridges and Judith Collins may be joined by ex-Finance Minister Steven Joyce and dark horse Mark Mitchell, a former policeman and hostage negotiator.
Mr Mitchell has reportedly been in Australia lately to support his daughter who's competing in a surf lifesaving competition, but is expected to reveal his intentions on Monday.
Both RNZ and Stuff report while he's clearly the lesser-known of the quintet, he's gathering support amongst the party's backbench MPs. Mr Joyce, who had a reputation as being the 'minister for everything' in the previous Government, has refused to rule himself out of a run.
Ms Collins is the only one of the five who has run for the leadership before, briefly putting her name forward after John Key's resignation but withdrawing when it became clear Bill English had the numbers.
She told RadioLIVE on Sunday if she led the party it would a "hell of a ride and so much fun", saying she'd go after "red meat" voters who don't read Vogue.
"I think Jacinda Ardern is utterly playing to her strengths. The Vogue shoots and all that. It's good for New Zealand. Good on her. She could be a fashion model, frankly."
The only one of the candidates so far who has MPs outwardly saying they'll vote for her is Ms Adams. She ruffled feathers in the race by announcing her candidacy flanked by MPs Nikki Kaye, Chris Bishop, Maggie Barry and Tim McIndoe.
In contrast, former deputy leader Gerry Brownlee told The AM Show on Monday it would be "not appropriate" to comment publicly on who he's backing.
"I'm not making any comment about who I'm supporting... Once it has run its course, then everyone will know who the new National leader is."
Asked why he wasn't running for the top job, Mr Brownlee said "not everyone can be leader".
"Any party leader - Jacinda Ardern for example, the current Prime Minister - has to be supported by very strong people inside or close in to her top team. That's how it works in New Zealand."
Asked to say something nice about Ms Collins, perhaps the most combative and divisive of the current contenders, Mr Brownlee said she was a "very forceful individual".
"I'd like to say something nice about all the candidates, because I think they're all very good people. I've known Judith for a very long time."
The last two times Labour has formed the Government, it's been with a woman at the helm. Asked if National needed a woman in charge to beat Ms Ardern, Mr Brownlee didn't directly say yes or no, but appeared to suggest Ms Ardern had been treated unfairly.
"I think it's very interesting just the way of Jacinda Ardern's pregnancy, and now Julie Anne Genter's... has been discussed sort of indicates a kind of, in a way, a gender bias in itself.
"Women will have made all the progress they need to make towards more equality when it just becomes something that happens, because it's a perfectly natural process."
- Greens leadership candidate Julie Anne Genter is pregnant
- Prime Minister Jacinda Ardern is pregnant, expecting child in June
Ms Genter is running for the Green Party leadership, and announced her pregnancy on Sunday afternoon. She has had two miscarriages in the past.
National will vote on its new leader on February 27.