The latest opinion poll shows the New Zealand First party close to the 5% threshold needed to get seats in Parliament without winning an electorate.
The Herald-DigiPoll survey has New Zealand First on 4.9%, its highest rating in the election campaign.
In the poll, released on Friday, support for most other parties is steady with National on 49.8%, Labour on 29.1% and the Green Party on 12.6%.
ACT is on 1.7% and the Maori Party, the Conservatives, the Mana Party and United Future are all below 1%.
The poll of 750 voters taken between last Thursday and Wednesday this week has a margin of error of 3.6%.
A 3 News-Reid Research poll released on Thursday also showed increased support for New Zealand First at 3.5%, though in a One News-Colmar Brunton poll its support was down, at 2.2.%.
In both surveys, there were slightly wider gaps between the two main parties. Support for National dropped slightly though the party was still above 50%, while support for Labour also dropped and was below 30%.
As support for the major parties fell, the Greens and some of the other smaller parties rose. The Green Party was on 13% in both polls.
Move to smaller parties at Labour's expense - Joyce
National Party campaign chairman Steven Joyce says the latest polling shows Labour's support is falling and there has been a move to third parties.
"You've had the minor leaders' debate this week, this is always the week of the campaign where minor parties get their opportunity to step up a little bit in terms of their visibility."
Asked about support from potential partners, Mr Joyce said all the small parties, including ACT, were getting a lift over the period.
"None of these things can be controlled by anybody because they are the electors' decisions. All we can do is .. say to people that we are determined to form a strong stable government after the election and how you want to assemble that is up to you."