Jacinda Ardern insists the trans-Tasman friendship with Australia is in fine health, and she won't join the international pile-on critiquing Scott Morrison's foreign engagement.

But nor is the New Zealand prime minister willing to support her Australian counterpart for recent dealings that have left France fuming, the USA cold and have further provoked China.

In a rare sit-down interview with Australian media, Ardern said she hadn't drawn any conclusions about Morrison's trustworthiness from the AUKUS episode, which upset a trio of world powers.

"I don't have to base the relationship on what I observe of others because I've got my own experience to base the relationship on," she told AAP from her Wellington office.

The two leaders' most recent dealing came last week, when New Zealand joined Australian forces in the Solomon Islands to diffuse tensions there.

"We do stay in regular contact ... and we don't schedule it, we just pick up the phone," Ardern said.

The trans-Tasman relationship is pivotal to New Zealand, which has one-fifth of Australia's population and a GDP seven times smaller.

Australia's centrality was demonstrated this week by new opposition leader Christopher Luxon, who was quizzed by TVNZ's Q and A program after taking the top job.

"Our most important relationship is that of Australia ... our economy is very tied to the success of Australia," he said.

READ MORE

• Australia and New Zealand unite over China human rights issues
• Australian Defence Minister's warning over prospect of war with China
• Can the rift be healed? Beneath the tension in the New Zealand-Australia relationship
• Norfolk Islanders want to ditch Australia for New Zealand

Ardern is an avid follower of Australian goings-on, referencing the vaccine rollout in Queensland and Covid-19 restrictions in the ACT during the interview.

She is acutely aware of the upcoming federal election, which could unite the Australian Labor and NZ Labour parties in office - which has happened for just one year of the past three decades.

She has an association with Australian opposition leader Anthony Albanese, having invited him to Wellington previously, and the pair maintain irregular contact but she insists she will "not jump into the politics" of Australia.

"Our relationship with Australia is so important to us that I will place a priority on making sure that there is a solid one with the prime minister of Australia, and we do have a solid relationship," Ardern said.

Still, her leadership has coincided with trans-Tasman tensions.

In February 2020 at a joint press conference in Sydney, Ardern summoned bravado rarely seen by a Kiwi prime minister to tell Morrison "do not deport your people or your problems".

And this February, she excoriated him again for wiping the Australian citizenship of a dual-national woman linked to Islamic State, leaving New Zealand to host her.

"If the shoe were on the other foot, we would take responsibility. That would be the right thing to do. And I ask of Australia that they do the same," Ardern fumed.

In Wellington this week, the prime minister said this was part and parcel of a close relationship.

"What you've seen there is us both speak openly and frankly, about our position on those issues," she said.

"You can see very transparently the positions that we've taken, because I will say privately what I will say publicly and so no one's left in any doubt about our view on those things. And actually, that suits us both."

Foreign policy-watchers either side of the Tasman believe the pair - of different generations, different genders and different world views - don't get along.

"We get along fine," Ardern said.

"We are from different political parties. And so that does mean we'll take different positions. But that hasn't stopped us from being able to make the relationship work well."