Hipkins teases Jacinda Ardern to make campaign appearance

Labour leader Chris Hipkins says he expects former prime minister Jacinda Ardern to make an appearance on the campaign trail "in the next few days".

It came as National and Labour were again at each other's throats over fiscal costings this morning and Hipkins defended the assumptions his party made in his policy plans.

Days away from the election, the Labour leader continues to face stagnating polling with growing expectations that Christopher Luxon could soon take up the ninth floor.

Hipkins said this morning that he thought his party had run a "very solid" campaign that he was "pretty proud" of.

"I actually think we've run a very solid campaign, and I'm pretty proud of our campaign."

The party leader then immediately pivoted to criticising National while reiterating Labour's attack lines that Luxon would institute deeper cuts if elected.

Brought back to Labour's poor polling, Hipkins said he thought there were still many undecided voters and that polls had been off in past elections.

"Actually, if we look at the polling and let's look at the last election, there was nearly a 10-point difference between what the final polls were showing literally days before the election, and what actually happened on election day."

When questioned, the Labour leader then hinted that Ardern would be making an appearance in the next few days on the campaign trail.

"I think we'll see a little bit more of Jacinda in the next few days. She's obviously in Boston, so the timezones make that a bit more challenging," Hipkins said.

It comes after former prime minister Sir John Key released a video on social media, imploring voters to support National and Christopher Luxon.

Labour appeared to respond in the days after with a video from former leader Helen Clark, however, so far, Ardern has been absent from this year's campaign trail.

Since resigning eight months ago, the former Labour leader and prime minister has kept away from national politics, instead choosing to focus on overseas initiatives.

She recently told a US interviewer that she "could have" kept going as prime minister, but stepped down as she felt she no longer had enough energy to do the "job well".

This morning, Labour claimed there was a hole amounting to hundreds of millions in National's fiscal plan — a suggestion Nicola Willis has deemed "not credible".

Willis said in response that Labour had failed to take into account some costs involved with its policies and that there was a blowout involved with Hipkins' GST-free fruit and vege policy.

Responding on Breakfast, the Labour leader said the suggestion was "plain wrong" and defended the costings of his flagship cost-of-living policy.

"We've set out our numbers. No one with economic credibility is saying our numbers don't add up. Some people are disagreeing with what we're proposing to do, but they're not saying that we've got our costings wrong."

Many economists have decried Labour's proposed GST-free fruit and vege policy as being too untargeted and tricky to implement.