NZ First, the party of political fixture Winston Peters, first elected in 1979, is struggling in the polls and could fade into irrelevancy when votes are tallied in the October 17 election.

On Thursday, Mr Peters was joined on stage in TVNZ's multi-party debate by leaders of four other parties - the Greens, high-flying libertarians ACT, indigenous campaigners the Maori Party and renegade force Advance NZ.

On current numbers, only ACT is assured of a place in the next parliament.

ACT leader David Seymour is certain to return to Wellington thanks to a deal with the National party, which runs dead in his conservative Auckland seat of Epsom.

Mr Seymour's rise has been stunning; under his leadership ACT's support has grown from just 0.5 per cent at the 2017 election to eight per cent in the latest poll.

The 37-year-old is a fresh-faced economic conservative who has made his name by championing the euthanasia referendum - and stunts like skydiving and appearing on Dancing With The Stars.

He was also the lone voice against Prime Minister Jacinda Ardern's assault rifle ban after the Christchurch Mosques shooting, drafting in a gun advocate to sit third on his ticket.

ACT has benefitted from the drop in support to National, the major conservative force, and Mr Seymour has often been the most cohesive voice of opposition to Ms Ardern's government.

"Having a genuinely independent team to hold them accountable is worth it, no matter which side the cookie crumbles," Mr Seymour told TVNZ.

The Greens, which holds ministries in Ms Ardern's government, are no certainty to return.

Thursday night's poll had the left-wingers down to six per cent, precariously above the five per cent threshold that secures seats in parliament.

"I'd be comfortable with a few more points than that, obviously," co-leader James Shaw said.

The Greens are supporting the popular PM, hoping to peel off enough left-leaning support with a pitch of improving the government.

"If the Greens don't make it back in, we do run the risk that one party will have all the power," he said.

In the squeeze, it's Mr Peters' party losing out.

NZ First has been polling at one or two per cent for months, the 75-year-old's case to Kiwis falling on deaf ears.

"For years we've defended vulnerable New Zealanders against political extremes ... experience and common sense is needed now in parliament more than ever," Mr Peters said.

"We're the best bet for stable government. So take out some insurance and party vote New Zealand First."

The Maori party is standing in the seven Maori electorates, notoriously hard to predict or forecast but with a chance of winning one or two.

For Advance NZ, polling at one per cent, they were lucky to share the state broadcaster's stage at all

The conspiracy theorists, which qualified for the debate through a technicality, are sceptical of 5G technology, COVID-19 vaccines and would open NZ's borders if in power.

Every party has ruled out working with them, and Mr Shaw produced the most memorable line of the debate when he told co-leader Jami-Lee Ross "not to believe everything you read on the internet".

Australian Associated Press