The Green Party has plummeted in the latest 1 NEWS Colmar Brunton poll to 4.3 per cent, leaving them below the five per cent threshold needed to return to Parliament.

The dramatic 11 point fall comes after the party's highest ever result in the previous 1 NEWS poll with 15 per cent, less than three weeks ago.

Meanwhile, the "Jacinda effect" has lifted the Labour Party to 37 per cent, up 13 points on the previous poll at the end of July. It's the highest result for the party since 2008.

National is down three points to 44 per cent of the party vote.

New Zealand First is down one point to 10 per cent, The Opportunities Party is steady on two per cent and the Maori Party is up one point to two per cent.

These results would leave neither National or Labour able to govern without the support of New Zealand First.

National's Bill English and Labour's Jacinda Ardern are tied in the preferred Prime Minister stakes at 30 per cent. Winston Peters is down three points to seven per cent.

The number of undecided voters is down seven per cent in this poll to 13 per cent.