A new poll shows New Zealand First list MP Shane Jones coming third in the contest for the Northland seat that's being seen as crucial to his party's chances of staying in Parliament.

The Colmar Brunton Poll for TVNZ's Q+A programme gives the incumbent National MP Matt King a firm lead, with 46 percent support.

Labour's Willow-Jean Prime has 31 percent support and Jones just 15 percent.

Eleven percent of respondents said they did not know who they would vote for, or declined to answer.

NZ First leader Winston Peters won the seat in a 2015 by-election, but was ousted by King in the 2017 general election.

The seat is seen as a must-win for New Zealand First, which a One News poll last month placed at 2 percent in the standings.

Jones told Q+A he needed to get the "political jackhammer" out, with his message to Northlanders that if they wanted to get NZ First back into Parliament they should vote for him or the party.

King said he was "heartened" by the poll result but was "taking nothing for granted".

Prime told the programme she was "really pleased to see that there is a huge level of support there, not only for myself but also for the Labour Party".

In terms of party support in Northland, Labour is at 41 percent, National 38 percent, ACT 8 percent, NZ First 7 percent and the Greens attract 4.7 percent, the poll has found.

Prime said it was the first time in recent history Labour was ahead of National in a poll.

A total of 503 eligible voters were polled and the margin of error is 4.3 percent.

Via rnz.co.nz