National was also in danger of losing more than 15 of its electorate seats – including several traditional strongholds.
They included Ilam, the Christchurch seat held by the party's deputy leader Gerry Brownlee since 1996. However, Brownlee would make it back in on the list if he decided to stay on, and Paul Goldsmith also seemed safe.
Collins and the National Party now face the big task of rebuilding for the 2023 election – and Collins could also face a leadership challenge if she goes ahead with her pre-election claim that she would stay in the job.
Brownlee said the swing was the nature of politics, but he would wait to see how the final result stacked up.
He acknowledged it was a bad night for his party, putting it down to Covid-19 rather than Collins' leadership or the campaign he had led. However, he said it was a long-standing party and would come back from it.
Other National MPs were less forgiving – Simon Bridges and Mark Mitchell both pointed to mistakes in the campaign, but both said Collins did not deserve to cop all the blame.
The final count and "special" votes, are unlikely to change Labour's election night result much: Labour usually picks up a seat on those votes.
Any fears that the Green Party would be squeezed out of Parliament by Labour's popularity were unfounded.
The party was on track to get about 8 per cent of the vote, and MP Chloe Swarbrick was also well-placed to win the Auckland Central electorate.
Green Party co-leader Marama Davidson congratulated Ardern for "an extraordinary win", and said the Greens were hoping to be part of a "strong, truly progressive government".
Ardern has said she would look to work with the Green Party regardless of whether Labour would govern alone.
While the night was a disaster for National, Act leader David Seymour was set to get about 10 MPs into Parliament.
The Māori Party was also in with a chance of getting back into Parliament – the contest between Labour's Tamati Coffey and Māori Party's Rawiri Waititi was paper-thin.
NZ First leader Winston Peters accepted his party's loss graciously, but gave no indication of what his future plans were.
He said his party had pledged to provide stability and certainty when it went into coalition with Labour and it had delivered on that.
He said there was still a need for a party that would challenge "the establishment".
"As for the next challenge, we'll all have to wait and see," Peters said.
Collins and Ardern were yet to speak at publication time.
Collins had to start from a standstill in July after the leadership changes from Simon Bridges to Todd Muller in May, and then to Collins in July after Muller stepped down.
That and a slew of resignations by high-profile MPs such as Paula Bennett and Nikki Kaye proved too much to come back from.
Ardern had hammered home the message of stability and certainty to voters in an election that was inevitably about who voters trusted most to contend with the Covid-19 environment – and was rewarded accordingly.
There were a number of close contests in the electorate seats, the results of which may not be known until after the special votes are counted in about a fortnight.
They included Auckland Central, in which Swarbrick and Labour's Helen White were neck and neck, and Hutt South which was close between National's Chris Bishop and Labour's Ginny Andersen.
