The Prime Minister has appeared unapologetic about taking her time to open the borders, defending the lack of a COVID-free travel bubble with the Pacific.
Cook Islands Prime Minister Henry Puna told Newshub earlier this month that without any cases of the disease, the Cook Islands poses no threat to New Zealand - and vice versa. Samoa, Kiribati, Nauru, the Solomon Islands, Tonga, Vanuatu and Tuvalu also haven't reported any cases.
New Zealand's last confirmed case was more than three weeks ago, and it's been four weeks since the last patient known to be infected via community transmission left self-isolation.
At one point Australia, like New Zealand, appeared to be crushing its outbreak - but has struggled to stamp it out completely, with new cases in the double-digits still turning up every day.
But Ardern told The AM Show on Monday that doesn't necessarily mean the Pacific will get first dibs on travel in and out of New Zealand, which blocked travel to most foreigners on March 19.
"What we need to see for any country that we make that decision around, regardless of whether or not we're talking about the realm countries - Cook Islands and Niue, versus Australia - a set of criteria that New Zealand needs to see in order for us to feel that both we're not running the risk of exporting any cases, and equally we're not seeing the risk of any coming in here.
"We've only been at level 1 for a week, so I am going to be cautious in that decision-making - unapologetically - because our borders are the reason that we now have the freedom that we have. If we move quickly or without making a full analysis of those decisions, we run the risk of losing everything. That's why we're going to be very careful here."
She spoke to Puna last week and said he had concerns that if New Zealand also opened up the border to Australia - where there are still hundreds of active cases - that would put his country at risk of importing the virus, which has killed 434,000 people around the world in a matter of months.
"The Cook Islands has to be happy to open with New Zealand, and also doing a little bit of thinking around whether or not they would be happy with the trans-Tasman arrangements as well. It's a bit of making sure we can make that whole system work when we open up those borders.
"Even if they say 'yes, let's open to New Zealand', if New Zealand has people coming in from a state of Australia, they have to be happy with that too. And we have to be happy with that."
Ardern, without naming any countries, said there were also concerns some other nations' borders weren't as tight as ours, with people perhaps able to arrive via porous maritime borders.
She wouldn't give a timeframe on when any bubble might be created, not wanting to get people's hopes up.
Epidemiologist Michael Baker of the University of Otago said the Government would likely wait until Australia's caught up before starting a trans-Tasman bubble.
"It would be so much easier to have free movement across the borders if we were all on the same page."
Infectious disease expert David Murdoch, also of the University of Otago, told The AM Show we need to stay at alert level 1 for now, including keeping the borders shut.
"It's very much dependent on how the rest of the world does. We're in new territory - there are many factors to consider in this."