The National Party's historic pollster has the party's support crashing to historic lows, while Act is on the verge of overtaking it.

A Curia poll, conducted for the Taxpayer's Union, has National on just 21.2 per cent, with Act close behind on 14.9 per cent.

The result is only a whisker above National's worst-ever election result, 20.93 per cent in 2002. It is the closest National and Act have ever been in the poll.

Labour is at 45.9 per cent with the Greens on 9.6. Te Paati Māori is on 1.2 per cent.

National's support has cratered in the poll. It was on about 30 per cent in July.

Jacinda Ardern reigned supreme as preferred Prime Minister on 50.8 per cent. National leader Judith Collins languishes at 4.4 per cent, well behind David Seymour on 9.3 per cent.

National would lose four seats on those numbers, down to 29. Act would get 19.

Labour would have 58 seats, and the Greens 12. Te Paati Māori would keep both its current seats.

The poll was conducted from Sunday September 5 to Thursday September 9, 2021, with the median response on Tuesday September 7, 2021. The sample size was 1,000 eligible New Zealand voters.

That period takes in a particularly difficult period for Collins' leadership. It includes the fallout from a difficult interview with TVNZ's Indira Stewart.

It was the second poll released on Wednesday, a leaked UMR poll, taken earlier in the lockdown painted a slightly less dire picture for National.

The UMR poll from August 31 to September 6 had Labour up two points to 45 per cent, and National back down to 26 per cent.

Act was holding steady on 13 per cent, and the Green Party was down 1 on 6 per cent. NZ First was at 4.1 per cent.

In early August, Labour was at 43 per cent in the same poll – its lowest result since February last year, before Covid-19 arrived.

There have recently been calls from within National for a change of leadership. Those calls could intensify on the back of this poll.