Reactions to tonight's announcement that NZ First will help Labour form a Government were mostly congratulatory - apart from one dire warning from the ACT party that a "madman" is now on the loose.
Laurell Ardern, the mother of Prime Minister-in-waiting Jacinda Ardern, was one of the first to publicly praise her daughter.
Speaking to Radio New Zealand's John Campbell from Niue, where Jacinda's father Ross Ardern is New Zealand High Commissioner, Laurell Ardern said she still "can't quite believe it's happened".
"I'm still coming to terms with it because, you know, she's just gone from the deputy, and she's just won the byelection in Mt Albert. Now this has happened. It's gone very fast," Ardern told Campbell.
Australian Prime Minister Malcolm Turnbull called Ardern tonight after Winston Peters' announcement, saying he was looking forward to continuing Australia-New Zealand relations.
Australia's Leader of the Opposition Bill Shorten tweeted "Congratulations @jacindaardern & @nzlabour - a new era for New Zealand" while fellow Labor MP and former Prime Minister Julia Gillard also tweeted her congratulations.
Auckland mayor Phil Goff - formerly Ardern's boss - has also welcomed the change of Government, though he said it would not be a magic wand that would suddenly resolve the city's problems.
"There will be a meeting of minds on what we need for transport...but the funding issues still need to be resolved."
National leader Bill English gave a gracious concession speech, wishing Jacinda Ardern well and saying he was one of very few who knew what a privilege it was to lead the country.
"I'm proud that as an outgoing Government we have left New Zealand in great shape by any international measure," he said.
"We wish the new Government well in taking the opportunity we have to build on the economic strength but also deal with longstanding issues that New Zealanders want to see dealt with."
But the Act Party's David Seymour has taken a darker view of today's proceedings, reiterating his view that any coalition with Winston Peters is doomed to fail.
"With no hints on policy, and vague attacks on 'capitalism', New Zealanders now face a weak left-wing coalition beholden to a madman on the loose," said Seymour, whose party won just 0.5per cent of the vote and faced being in Opposition even if Peters had sided with National.
New Zealanders now face a "big-spending, tax-everything-that-moves, 1970s-protectionist, red-tape-loving Government", he said.
But he said the silver lining was that Peters had caused chaos in every government he had joined and the "perverse marriage" of Labour, NZ First and the Greens was likely to implode.
Erstwhile United Future MP Peter Dunne appeared to agree, tweeting to Green Party leader James Shaw that he was now tasked with keeping his "unruly new partner" in line.
Dunne also congratulated Ardern on her win.
Greenpeace executive director Dr Russel Norman said he was cautiously hopeful about the environment under a Labour-led government.
Norman called for an immediate halt to the Block Offer - the annual tender for new petroleum exploration - and said Greenpeace would also be lobbying for better irrigation and farming practices.
E tū, the biggest private sector union in New Zealand and a Labour affiliate, was "ecstatic" about the decision, which it said signalled a better deal for working families. Many members had campaigned hard on behalf of Labour and the Greens, national secretary John Ryall said.
The Council of Trade Unions also welcomed the new government, with secretary Sam Huggar saying the CTU was excited to have a coalition government committed to lifting incomes, equal pay for women and ending poverty.
"Let's not kid ourselves, as well as a fiscal deficit, there is a social and infrastructure deficit after 9 years of austerity," Huggard said.
"It might not be properly measured, but it's visible in the state of our housing, our rivers and stagnant productivity in our workplaces. The high election turn-out was a sign that New Zealand is re-energised by a change to our political landscape. Working people finally have hope that their time and energy will be better valued by those in power."
ILGA Oceania - which represents lesbian, gay, bisexual, transgender and intersex organisations in New Zealand, Australia and the Pacific - said it was excited to welcome Labour and the Greens to power as they had campaigned to improve human rights for LGBTI groups.