The latest One News Colmar Brunton poll has seen National's popularity drop by one point, but Labour has not moved in the past week.
The poll of 1,000 people, released on Sunday, puts National at 51% and Labour on 33%.
National's loss may been the Greens' gain, with that party moving up one point from last week to 8%.
No other minor party reached the 5% threshold on party votes.
The poll has a margin of error of plus or minus 3.1%.