Australia has been warned it could be asked to leave the Pacific Islands Forum (PIF) if it does not start supporting stronger action on climate change.
Kiribati president Anote Tong warned people in the region would have to flee in waves similar to the current migrant crisis in Europe unless stronger action was taken to reduce emissions.
"I think it would be incumbent on them because how relevant [would] their presence be," he said.
"We expect them as a our big brothers, not bad brothers, our big brothers to support us on this one."
Australia and New Zealand are the two most economically powerful members of the PIF, which is meeting this week in Port Moresby.
Pacific nations have called to limit global temperature increases to 1.5 degrees Celsius, saying the current goal of 2 degrees above the pre-industrial level would push many beyond their ability to adapt.
Mr Tong's comments follow similar remarks he made on Monday that Australia and New Zealand should show they were "real friends" by supporting more action on climate change.
Kiribati, with its population of 110,000 spread across 33 low-lying islands, is particularly vulnerable to climate change.
Prime Minister Tony Abbott will travel to Port Moresby on Wednesday and will take part in the main PIF leaders retreat on Thursday.
On Tuesday, Mr Tong invited Mr Abbott to visit Kiribati to see the impacts of climate change for himself.
"I'd love for him to have him come and stay for the rest of his life," he said.
Pacific nations are expected to called for a ban on new coal mines and more ambitious targets for limiting global temperature rise when leaders meet at the regional summit on Thursday.