Long-time National MP Judith Collins emerged victorious in tonight's leadership vote and is determined to win back the treasury benches come September 19.
And she has set her sights on Prime Minister Jacinda Ardern.
"There is no chance at all that I'm going to let Prime Minister Jacinda Ardern get away with any nonsense when it comes to the economy and doing her job. We will hold her to account."
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Gerry Brownlee was elected deputy leader in a crisis caucus meeting which lasted more than two and a-half hours.
The pair were flanked by what looked to be every National MP at Parliament this evening.
Speaking to media, she talked up her MPs – gesturing to them when describing her front bench.
"I can tell you that our team is better than their team," she said.
She said the Prime Minister had only three ministers that she had confidence in – whereas she had a whole team.
"I am hoping that the National Party will collectively crush the other lot, come September 19," she said, when asked if she could shake the nickname 'Crusher'.
Asked about her first job as National leader, Collins replied: "Winning".
"My focus as leader will be helping rebuild our communities and dealing with the economic and jobs crisis by getting Kiwis back to work," she said.
"Only National has the experience and skills to get us through this. We are a strong team and I look forward to forming the next Government."
New Zealand's economic recovery and what she suggested was an incompetent Government was a theme of Collins' late-night press conference.
"We're just going to have the most fun as we take back the country."
But she did concede it would be hard work – there are just 66 days until the election and the campaign period is only weeks away,
Collins warned that Ardern should not be underestimated.
Asked what she had over Ardern, she said: "Experience, toughness and the ability to make tough decisions."
Collins would not talk about who else ran for the leadership, or the deputy leadership.
Tonight was her third crack at National's leadership.
She put her hand up to replace John Key after he resigned as Prime Minister in 2016.
After it became obvious that Bill English – who was Key's preferred choice – had the numbers, she withdrew herself from consideration.
When Bill English resigned as National leader in early 2018, she – along with fellow National MPs Mark Mitchell, Simon Bridges, Amy Adams and Steven Joyce – ran for the top job.
She lost to Bridges, polling the lowest.
"It's third time lucky," she said, when asked about the leadership run.
She confirmed there would be a minor re-shuffle in the next few days or weeks.
But finance spokesman Paul Goldsmith would keep his portfolio.
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When asked about Michael Woodhouse keeping his health portfolio, Collins said there were "still a few things to work out".
She also confirmed that none of the MPs who had previously announced they were resigning from politics, such as Paula Bennett, have indicated they would be coming back.
And other caucus decisions – such as ruling out working with NZ First after the election – still stand, she confirmed.
National's policy base will be largely unchanged, she said.
"We're a serious party, with serious policies," she said.
Her focus now was to start winning back the confidence of National's base.
"It's important that we send some strong messages out to our base," she said.
That base has been a bit "discombobulated".
After concluding the press conference, Collins said "I think it might be time for a drink," before posing for a few photos and leaving with her team.
The caucus meeting to decide who replaced Todd Muller started at 7pm.
There were reports of a contest for the leadership.
Rodney MP Mark Mitchell was understood to be considering a tilt, as was Hutt South MP Chris Bishop.
Collins came into Parliament in 2002. She is the party's first female leader since Jenny Shipley departed in 2001.
Fifty-three days ago, Collins said she voted for Muller as leader because she thought it was "the best course" for the party.
She believed he was best placed to make sure her colleagues on National's list kept their jobs after the election.
"I have been very successful in voting for the right leader every time," said Collins at the time.
Earlier tonight, MediaWorks reported former leader Simon Bridges was not entering the leadership race, and that Mitchell and Louise Upston have formed a team to bid for the top jobs.
MP Melissa Lee said the caucus would select its new leader tonight, RNZ reported.
At 8.30pm, clapping was heard from the caucus room.
Louise Upston told media after landing in Wellington that Muller's resignation had come as a "total shock".
"It's a real shock - there's no two ways about it. My thoughts are with him and his family and as the National Party caucus we've got a job to do to fill that gap."
Upston said she didn't think caucus would be "rushing" their decision.
"It's really important for the country to know the National Party has their best interests at heart and so we will be selecting a leader that we believe has the attributes and ability to lead our fantastic party for now and in the future."
Long-time MP Gerry Brownlee might also be an option for the deputy role, as is finance spokesman – and Bridges backer – Paul Goldsmith.
Current deputy, Nikki Kaye, is likely to be chairing tonight's meeting.
She would not be drawn on whether she would put herself forward for leader, or deputy leader, or who she'd support.
There is no script as to how tonight's meeting will run, but there is every chance a new leader will emerge tonight.
Speaking to reporters on the way into Parliament this morning, Mitchell said tonight's caucus meeting was about deciding on a process to follow.
"There may be an outcome tonight, there may be one tomorrow – we will have to wait and see."
This morning, Muller announced he was stepping down as National leader – a position he has held for less than 60 days.
"The role has taken a heavy toll on me personally, and on my family, and this has become untenable from a health perspective."
The shock resignation led to a wave of speculation as to who would be taking over.
The clear front runners are Bridges – who Muller rolled as leader in late May – or Collins.
Both have run for the leadership before – Collins twice.
The pair squared off after Bill English stood down in early 2018; Bridges won that contest.
But neither MP was giving much away this morning.
Bridges ignored questions as to whether he was running for the leadership.
Speaking to reporters at Auckland Airport, Collins said "I'm going to keep all of my discussions within caucus" when asked the same thing.
Asked if she had been waiting a long time for her shot as leader, Collins said today was "just another day".
National MPs learned of Muller's resignation on a call this morning at 7.30am. Moments later, a media statement was released.
The party's senior whip, Barbara Kuriger, said she did not know whether Muller would be in Wellington for tonight's meeting.
National MPs have been making their way back to the capital all day.
Almost all MPs door-stopped by media at an airport, or in front of Parliament, today sent Muller and his family their sympathy and best wishes.
"The important thing is we have compassion for Todd at this time while we work through what has been a very difficult time," Kaye said this afternoon.
Speaking to reporters in Wellington airport, Paula Bennett – who announced earlier this month that she would not be contesting the election – would only say the caucus has a "big decision to make".
She said she had "no comment to make about anything", when repeatedly questioned on today's developments and what will happen tonight.
But she did say: "These are just difficult times for the party and the caucus – so we are just going to work our way through that respectfully."