Ms Clark knows a thing or two about winning elections.

The 70-year-old won three in 1999, 2002 and 2005, and believes Ms Ardern is on track to emulate the biggest poll success of her career.

"It feels a lot like the 2002 election," Ms Clark told AAP in Auckland.

"It's too late for anything to blindside Jacinda's express train now."

The latest poll figures confirm a booming win for Labour is likely.

A TVNZ-Colmar Brunton poll published on Thursday night showed Labour on 46 per cent (down one), and opposition National on 31 per cent (down one).

Replicated in parliament, Labour would send 59 MPs to the 120-seat house - two shy of a governing majority.

No party, not even Ms Clark at the height of her popularity in 2002, has been able to achieve a majority since electoral reform in 1996.

Then, Ms Clark returned 52 MPs as National crashed to a historic low of 21 per cent - the worst performance in the party's dominant history.

Ms Clark believes a majority could be within Ms Ardern's grasp.

"She might. She could," she said.

"Jacinda has run an extremely successful campaign. It's been an amazing campaign.

"I've been very impressed by Jacinda's restraint. She's been niggled at, sniped at continually and she's never lost her dignity or her calm. It is remarkable.

"The campaign has gone extremely well. Not all campaigns are going so smoothly ... the National campaign has got worse each now and it's getting so clearly desperate.

"People have made up their minds. The issue will be how much wasted vote there is. You could get a majority off 47 per cent of the vote. It's entirely possible."

Ms Ardern's opponent, Judith Collins, has run an increasingly erratic campaign in the final weeks, lashing out at obese Kiwis and even the state of Tasmania.

Ms Collins' primary arguments - that National will tax Kiwis less and improve government delivery - have failed to catch fire, in the wake of Ms Ardern's impressive handling of COVID-19.

Ms Collins has faced an uphill battle in her short tenure.

With National already behind in the polls, she took the job in July when leader Todd Muller resigned unexpectedly on mental health grounds.

And Kiwis do not turf first-term governments; not since the 1970s have New Zealanders decided not to give new prime ministers at least one more go.

Ms Clark said it all contributed to Labour's likely success.

"This is an election like no other in our lifetimes. It's an election in the backdrop of an existential threat to everyone in New Zealand," Ms Clark said.

"It doesn't surprise me that the unusual context looks likely to produce a result which we could not have predicted when we came into this year.

"I still predicted a win for Labour but not on this scale. Normally you don't get something on this scale."

While Labour is set to claim victory, National will spend another three years wallowing in opposition.

Matthew Hooton, a long time National-aligned strategist who helped Mr Muller to the top job this year, said another defeat in 2023 beckons without a re-think of party direction.

Ms Collins, who is not resigned to a loss, has pledged to stay on as opposition leader after Saturday.

Australian Associated Press