The Labour Party will hold its campaign launch today with its own poll putting it just three points adrift of National - and bringing heartening news for Labour's potential support partner the Greens.

The Herald has seen the latest poll results from UMR - Labour's polling company - for a poll which ended on August 17.

That had National down three points from the week before to just 40 per cent - although the UMR poll traditionally has National at a lower level than most public polls.

Labour was up one point since the week before to 37 per cent - the same level of support it had in the One News Colmar Brunton poll released this week.

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The polls are a good platform for Labour to launch its campaign today at the Auckland Town Hall.

The launch is tipped to see the return of the prodigal former PM, Helen Clark, to the Labour stage after almost a decade of staying clear of domestic politics while she was head of the UN Development Programme.

Clark is back in the country and on Friday became a patron of Refugees as Survivors New Zealand.

However, while the Green Party was on 4.3 per cent in that Colmar Brunton poll - below the 5 per cent threshold to return to Parliament - it had stayed steady on 8 per cent in the UMR poll. That is still well adrift of the 11-15 per cent it was at in both UMR and Colmar Brunton prior to the resignation of Metiria Turei and election of Jacinda Ardern as Labour leader.

NZ First was also holding strong - up one to 9 per cent - and would still likely be the kingmaker on those results.

The poll shows less movement among the smaller parties than the Colmar Brunton. As Labour closes the gap with National it is expected the large parties will dominate, potentially squeezing down the medium and smaller parties as voters move to shore up their own side rather than toy with a strategic vote.

The move down for National in the UMR over the space of the week is similar to that in the Colmar Brunton poll in which National dropped from 47 to 44 per cent. The drop in both will worry National as it contends with the buzz around Labour leader Jacinda Ardern.

In National's favour, the majority of people were still optimistic about the country's direction - 56 per cent to 35 per cent negative.

However, Ardern's first two weeks in the job had impressed voters - her favourability rating was 70 per cent to Prime Minister Bill English's 57 per cent. And only 10 per cent viewed her unfavourably compared with 37 per cent for English.

Ardern is not expected to announce any campaign policy in her first major speech to the Labour faithful as leader but rather to focus on leadership and rally the troops for the campaign.

• The UMR poll canvasses 750 voters and has a margin of error of +/- 3.6 per cent.