Winston Peters an early favourite for Northland byelection - poll

New Zealand First leader Winston Peters, has the words 'Follow Me' on the back of his campaign bus. Photo / NZME.

The first poll of the Northland byelection shows NZ First leader Winston Peters has taken an early lead - the 3 News Reid Research poll has him ahead of the National Party candidate after the first week of the campaign.

The 3 News Reid Research poll of 500 Northland voters had Winston Peters on 35 per cent while National's Mark Osborne was on 30 per cent. Labour's Willow Jean Prime was on 16 per cent while 11 per cent chose other candidates or did not know.

It would be a massive upset if the results translated into reality on March 28 when the byelection is held - and makes a mockery of Prime Minister John Key's statement that Mr Peters had "zero" chance of winning.

National has held the seat for decades and had a majority of more than 9,000 votes in the election last year. The byelection was sparked by the resignation of former MP Mike Sabin, following reports he was under Police investigation.

The poll also also indicates there is some discomfort about the circumstances and National's handling of the resignation of Mike Sabin. Asked whether voters should have been told Mr Sabin was under investigation, 71 per cent said yes - including half of National voters.

The poll comes at an early stage of the contest during which Mr Peters has had a lot of media attention. Mr Osborne was only selected as National's candidate on Sunday and is still a relative unknown.

Small polls on individual electorates can be unreliable but the results indicate the contest is closer than National will be comfortable with, especially if a second poll on TVNZ's Q+A programme on Sunday is similar.

It will also reignite talk about whether Labour should signal to Labour voters to vote for Mr Peters instead of Ms Prime to help NZ First take the seat from National.

In a further ego boost for Mr Peters, those polled rejected Prime Minister John Key's insinuation that Mr Peters, at 69, was at the end of his career and would effectively be a one-term local MP.

Asked whether Mr Peters was too old to be the electorate MP, 85 per cent said no. If Peters wins the seat NZ First will get another list MP and National will no longer be able to rely on either Act leader David Seymour or United Future's Peter Dunne to pass legislation that is not confidence and supply.

Northland byelection poll, 3 News Reid Research:
Winston Peters, NZ First: 35%
Mark Osborne, National: 30%
Willow-Jean Prime, Labour: 16%
Other/Don't know: 19%
* poll of 500 eligible Northland voters was taken from 2 - 4 March and has a margin of error of +/- 4.4 per cent.