Fiji's prime minister Frank Bainimarama says people who leave Tuvalu and Kiribati because of climate change will be allowed to settle permanently in Fiji.
In a speech at climate action talks in Suva he said he expected the United States to do the same for Marshall Islanders because of their historical ties.
The island groups are low lying and already suffering from sea level rise.
Mr Bainimarama said the i-Kiribati and Tuvaluans "will not be refugees" and he promised that Fijians would take them into their homes and hearts.
"And we ask other countries to offer the same hospitality to anyone who is displaced by climate change. Because ultimately, we are one world, one people," he said.
Regional leaders and climate experts have gathered in the Fijian capital for two days of talks at the Climate Action Pacific Partnership event.
The event is aimed at helping the region's small island developing states take part in plans for global climate action.