Prime Minister Jacinda Ardern will be attending the leaders' meeting of the Pacific Islands Forum this week, amid what's been billed as a "crucial time for the region".
Nauru has also confirmed it will not attend due to a Covid-19 outbreak on the island, while the Marshall Islands will miss the forum due to legal issues.
Ardern will be in Suva from Tuesday to Thursday and will be in a range of meetings throughout the week, culminating in the traditional leaders' retreat.
She is also expected to make announcements on climate and aid projects and hold bilateral meetings with a number of Pacific leaders.
"This meeting is about us as a Pacific region establishing our own priorities and working together collectively to achieve them," Ardern said.
With a large Pasifika population in New Zealand, the challenges the Pacific region faces are New Zealand's too, she said.
"This meeting comes at a critical time for the Pacific, with the region facing climate, environmental, governance, and human development challenges, as well as sharpening geostrategic competition.
"New Zealand is committed to the forum as the primary vehicle for addressing these challenges."
Speaking about Kiribati's decision on Monday, Ardern told Breakfast leaders had been trying to persuade the country to stay and that there had been issues for some time already.
"Of course, [Kiribati] also signalled that they wish to work with the forum on critical issues such as climate change.
"Ultimately, I will leave it to the forum to speak to forum unity. For our part, of course, we would love for there to be that total membership - it is so critical at this time. But that doesn't stop us from being to work together," she said.
It comes days after Ardern's major foreign policy speech in Australia, in which she asked that the same worry about the militarisation of the Pacific region be matched by a concern for low-lying islands experiencing "the violence of climate change".
National's foreign affairs spokesperson Gerry Brownlee said Kiribati's withdrawal and Micronesia's non-attendance are worrying.
"The Prime Minister should concentrate her efforts this week on resolving the issues that have seen Kiribati withdraw from the forum and Micronesia decide not to attend. Failure to do so will render the forum a toothless organisation," Brownlee said.
“The Pacific Island Forum has been heralded as being an opportunity to patch up disagreements among the nations in attendance. But the breakdown of the Suva agreement before the forum is extremely concerning."
It's the first time Pacific leaders will meet face to face since 2019. This year, they will be seeking the endorsement of the Blue Pacific Continent strategy, which looks to the region's priorities to 2050.
The forum will be chaired by Fiji's Prime Minister Frank Bainimarama.
1News Pacific Correspondent Barbara Dreaver told Breakfast Kiribati's choice to leave the forum is "incredibly sad" because its citizens deserve to be represented in the region.
"Never before has the forum faced such a crisis. The reason why it is a crisis is because regionalism is playing such a big role at the moment with not just China but other countries' geopolitical interests in the region."
Regardless, work will be done around the Blue Pacific Continent strategy, Dreaver said.
The newly elected Australian government will also be pushed to do more for climate change, she added.
Dreaver said the forum was about Pacific Island nations presenting a united front on the international stage.