Act leader David Seymour is now twice as popular as his National counterpart Judith Collins.
The latest 1 News Colmar Brunton Poll, showed Seymour polling 11 per cent as preferred prime minister, up 5 points.
Collins is on 5 per cent, having fallen 4 points.
Close behind Collins are National rivals Christopher Luxon, on 3 per cent, and Simon Bridges, on 2 per cent.
Prime Minister Jacinda Ardern is on 44 per cent - down from 48 per cent.
The poll painted a miserable picture for both main parties, with Labour falling 3 points to 43 per cent and National falling 3 points to 26 per cent.
The only big winner was Act, which rose 5 points to 14 per cent
The Greens and Te Paati Māori were steady on 8 per cent and 2 per cent respectively. NZ First was up 2 points to 3 per cent.
Those results would translate into 55 seats for Labour, who could govern comfortably with the Greens, who would have 10 seats.
National would have 34 seats and Act would have 18. Te Paati Māori would get an extra MP, giving it three seats.
The poll sampled 1001 eligible voters between September 22 and 26 and has a margin of error of 3.1 per cent at the 95 per cent confidence level.
Collins said a leadership change was not on the cards for National.
"I think it's really clear the party has had four leaders in a very short period of time, that is clearly not a solution," she said.
The numbers are the lowest Labour has polled for months. The party was at 49 per cent in March.
But Ardern said the numbers were "strong".
"These are strong numbers that speak to a confidence in the plan that we have. These have been a tough couple of months for New Zealanders," she said.
Seymour said his bounce was down to "voters ... responding to people offering a pathway out of Covid".
This poll is the third in recent weeks to paint a grim picture for National.
A Talbot Mills (formerly UMR) Poll taken between August 31 and September 6 had Labour at 45 per cent and National at 26, with Act on 13. The Greens and Te Paati Māori were on 6 and 2 per cent respectively.
The worst poll came from National's own pollster, Curia. A poll taken for the Taxpayers Union between September 5 and 9 had Labour on 45.8, with National languishing on 21.3.
Both of those polls also had Seymour beating Collins as preferred prime minister.
Collins has had a tough fortnight as leader, rocked by speculation a leadership coup might be imminent.
Last week, she vowed to fight on as National leader, saying she will never resign from the job.
"I feel very secure in [the leadership] and I know the caucus is working very hard with a common goal of holding this Government to account," she said.
In a 2018 interview, when she was vying for the leadership in the wake of Bill English's resignation, Collins said she would resign if her polling fell below 35 per cent.
"Once things start getting under 35 per cent people start saying 'Can we win?' And I know I am putting a mark up there which at some stage in the future, if I am successful this time, that people will say 'Well, you set that mark," Collins said in that interview.
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