The latest opinion poll shows National at 41 per cent support, it's lowest level in three years, while Labour has jumped eight points to 33.5 per cent.

The just-released Roy Morgan poll has National down 4.5 points in a month.

The results are in stark contrast to a One News Colmar-Brunton poll on September 17 which showed National strong and steady on 48 per cent while Labour had fallen to 26 per cent.

Labour leader Andrew Little refused to accept the results of the One News poll and released his party's private polling which put National at 40 per cent.

Wednesday's Roy Morgan poll shows a Labour/Greens alliance would hold 45.5 per cent, but NZ First on 8.5 per cent would still hold the balance of power.

The Greens were on 12 per cent, down 2.5 points, and NZ First's 8.5 per cent was a fall of one point.

There was little change in minor party levels of support.

The Roy Morgan poll is more volatile than others, and usually shows strong swings.