Everything has changed and nothing has changed.

Labour's new leader Jacinda Ardern has managed to make New Zealand politics as gripping as the dramas in the United States and Britain that captured world attention.

But Winston Peters' New Zealand First is still likely to determine who will form the next Government, according to TV1's Colmar Brunton poll, the first one that has taken in all the recent catastrophes in New Zealand politics.

Prime Minister Bill English would be able to form a National-led Government only with NZ First.

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Prime Minister Jacinda Ardern would be able to form a Labour-led Government but would need New Zealand First, and another party.

Neither could form one without Peters, although it could be a very close-run thing.

That fact alone may force less committed supporters away from New Zealand First and into their blue or red corners, making it more of a contest between the two big parties than New Zealand has seen in previous MMP elections.

The results are devastating for the Greens. They are being punished for many things in the past five weeks but disunity is top of the list, or as leader James Shaw calls it, "messiness".

He is now under immense pressure, in a bid to rescue the party from oblivion.

Shaw has never fought an election as leader. But then, neither has Ardern, and it hasn't done her any harm. Eating the Greens has given Labour the healthiest poll result in years.

Ardern's equalling English in the preferred PM stakes is a stunning result. She was almost certainly helped by the Australian Liberal deputy Julie Bishop's furious intervention into New Zealand politics, and threats against Labour.

Ardern handled it deftly, as she did her own party's leadership crisis, and the Green Party's leadership crisis.

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We get the picture. She can do crises. We are about to see if she can handle the grind of the campaign.