Anthony Albanese will fly out to Palau on Monday to attend the Pacific Islands Forum at a time of growing tensions in the region.
But Solomon Islands Prime Minister Matthew Wale will be a no-show at the event, after a no-confidence motion was lodged against him by Home Affairs Minister Manasseh Maelanga.
Australia has been in negotiations with the Solomons on a security treaty, with the hopes further negotiations could have taken place on the sidelines of the summit.
Fiji Prime Minister Sitiveni Rabuka and his Vanuatu counterpart Jotham Napat will also not be attending, with Samoan leader La'auli Leuatea Schmidt another notable absence.
Mr Albanese's travel plans will be unchanged, despite the late withdrawals.
The prime minister earlier on Sunday said Australia had a duty to help Pacific nations thrive.
Mr Albanese said allowing Pacific nations to succeed would also benefit Australia.
"The big challenges facing the Pacific require solutions designed and delivered for the Pacific, by the Pacific," he told the Queensland Labor conference on Sunday in Brisbane.
"Australia has a key role to play, as a partner and leader.
"In a time of strategic competition in our region, our engagement in the Pacific Islands Forum and our contributions to the infrastructure, regional security and climate action of the region matter more than ever before."
The visit follows the prime minister signing a security deal with Fiji, elevating the bilateral relationship to a formal alliance as Australia seeks to curb Chinese influence in the region.
Pacific leaders are set to discuss security and climate concerns during the summit.
Mr Albanese said Australia would also seek to reiterate support for Pacific workers coming to the country.
Debate has recently raged over how the Pacific Australia Labour Mobility Scheme cohort would factor into immigration cuts flagged by various parties.
Representatives of the resurgent One Nation have been pressed to clarify that PALM workers, many of whom provide much-needed labour in regional areas, would not be included in a significant reduction to net overseas migration.
Mr Albanese said the migration discussion had been fuelling division and the Pacific worker scheme would continue because of its critical economic benefit.
"People from the Pacific make an enormous contribution to Australia's prosperity through their vital work in regional industries like agriculture and meat processing," he said.
"So many of our farmers and food producers rely on them.
"We know also the wages they remit home help boost the economies of their families and communities, contributing to the prosperity and stability of the whole region."
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