The latest Roy Morgan Poll shows support for the National Party has fallen two per cent since early June.
However the party is still the clear leader on 45.5 per cent, ahead of the Labour Party, which is up half a per cent to 32.5 per cent.
It's the closest the two parties have been in the poll since May last year.
The Green Party is up another per cent to 13 per cent, while support for the minor parties has changed only slightly.
If a general election were held today, the poll suggests the result would be too close to call.