Solomon Islands, Papua New Guinea and the Federated States of Micronesia have submitted a joint continental shelf claim on the Ontong Java plateau to the United Nations.
The plateau is the world's largest igneous rock of roughly the size of Alaska, which was formed about 120 million years ago.
The submission relates to scientific data showing the plateau is located outside these three countries' economic exclusive zones.
The three countries' United Nation's representatives heralded the submission as a historical milestone and a testament for practical regional cooperation.
The Cook Islands has also lodged a claim to extend its continental shelf last month.