Jacinda Ardern's reaction to Judith Collins rising to the top of the National Party

Judith Collins has risen to the top of the National Party following Todd Muller's resignation - but Prime Minister Jacinda Ardern says she has more important things to worry about. 

In her maiden speech as National leader on Tuesday night, Collins said she would not let the Prime Minister get away with any "nonsense" and said she would "take the fight" to the Government at the election. 

"I think it's important we give credit where it's due. But at the same time, there is no chance at all I'm going to let Prime Minister Jacinda Ardern get away with any nonsense when it comes to our economy and doing her job," Collins said.

"I will hold her to account."

But the Prime Minister would not be drawn on whether Collins is a threat. 

"I think it's fair to say that I've been spending more time thinking about New Zealand's response and economic recovery from COVID-19," she said on Wednesday. 

"I absolutely accept that there is an election this year and there is no avoiding that. But at the moment, really it's taking a bare minimum of my thinking because we are still in the middle of a global pandemic."

Ardern said Collins is her fourth National Party leader opponent. The Labour Party leader has been up against Bill English, Simon Bridges, Todd Muller and now Collins. 

"I have to admit that I don't really sit down and analyse them all. My focus, my time, my energy is going into our COVID response and that's as it should be," Ardern said. 

"I accept there will be politicking this year, I accept we have an election, but if I'm being brutally honest, my mind hasn't been particularly focussed on that to date."

Ardern said Kiwis want to see that she's focused on the "things that matter" to them. 

"I think right now politicking doesn't matter much to them. They want to know that we're focussed on COVID and I can assure them we are."

Right-leaning political commentator Trish Sherson told The AM Show Ardern should be worried about Collins and her deputy Gerry Brownlee, because they looked more confident than the previous leadership team of Muller and Nikki Kaye. 

"The difference between when Judith and Gerry emerged from that caucus room last night to 54 days ago when Nikki and Todd emerged. Nikki and Todd came out and they were frowning, they looked uncertain."

Sherson said Collins has been effective at picking apart the Government's undelivered promises, such as KiwiBuild. The housing programme's failure to live up to initial targets led to the demotion of former Housing Minister Phil Twyford. 

"That's why I think if I were Jacinda, I would be worried," Sherson said. "I would be looking at what happened to Phil [Twyford] and going 'now it is my turn'."

But left-leaning commentator Chris Trotter isn't so sure Collins will end up taking National into Government, suggesting she is only there to keep the party base happy and retain as many seats as possible. 

"It does really have the character of a Hail Mary pass for National. She's tried, she failed, she's tried, she failed. Now that the party is in dire straits they reach for her as a drowning man would reach for a lifebuoy."

The latest Newshub-Reid Research poll had Ardern at 59.5 percent as preferred Prime Minister - but that was when Simon Bridges was National Party leader.  

Collins wasn't leader then and yet she still made an appearance at 3.1 percent.