The Labour Party has soared to 33 per cent under new leader Jacinda Ardern in a new poll while the embattled Green Party's popularity has plummeted.

The result from the Newshub-Reid Research poll follows an extraordinary month in politics in which Jacinda Ardern took over as Labour leader, and Green Party co-leader Metiria Turei came under intense pressure after her benefit fraud admission caused two MPs to resign.

Compared to a poll nine days ago, Labour has risen from 24.1 per cent to 33.1 per cent, while the Greens have fallen from 13 per cent to 8.3 per cent.

National is only slightly down 0.8 per cent to 44.4 per cent.

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New Zealand First drops 3.8 per cent to 9.2 per cent - pushing the Greens out of position to become the third most popular party and still holding the balance of power.

On the preferred prime minister question, Ardern increased a stunning 17.6 per cent to 26.3 per cent.

That is not far behind Bill English who has edged up 1.9 per cent to 27.7 per cent.

Winston Peters has dropped 1.9 per cent to 10 per cent.

Of the minor parties, Gareth Morgan's The Opportunities Party is on 2 per cent (no change), with the Maori Party up slightly to 1.5 per cent. Act is 0.6 per cent and United Future 0.1 per cent.

Translated to seats in Parliament, National on 55 cannot form a coalition government with its support partners. Neither can Labour (41 seats) with the support of the Greens (10) - New Zealand First holds the balance of power with 11 seats.

The poll's release comes less than an hour after Turei announced she was standing down as co-leader and likely to leave Parliament after the election.

National's campaign chair and Finance Minister Steven Joyce said Labour's huge gain in the Newshub poll wasn't a great surprise.

"You saw the numbers coming off both New Zealand First and the Greens. Actually I genuinely thought the Greens might be a little bit lower than that after the weeks that they have had."

He said he wasn't worried about Ardern's remarkable rise in the preferred prime minister stakes, saying she was always going to get a honeymoon period and the focus would soon be on policy.

Ardern said the poll results were heartening, "but we're not going to be resting on our laurels - absolutely not".

The Herald can also reveal leaked results from the latest UMR poll, which finished today. That shows Labour has surged from 23 per cent a fortnight ago to 36 per cent. Support for the Green Party collapsed from 15 per cent to 8 per cent.

In the UMR poll support for New Zealand First dropped from 16 to 8 per cent. National went up 1 per cent to 43 per cent.

Since the previous Newshub-Reid Research poll on July 30, Labour leader Andrew Little quit as leader and was replaced the same day by Ardern in an uncontested vote. Over the same period, the Green Party fell into crisis after as Turei's handling of her benefit controversy prompted two Green MPs to resign.

The Newshub-Reid Research poll was conducted from August 2 to yesterday, and has a margin of error of 3.1 per cent. It uses a mixed methodology - 750 people are surveyed using landlines, and 250 on an internet panel.