WASHINGTON (AFP) - United StatesPresident Barack Obama will travel to his native Hawaii on Wednesday (Aug 24) to establish the world's largest marine reserve and burnish his environmental legacy.

The outgoing president will announce a massive expansion of the Papahanaumokuakea Marine National Monument across a swathe of the Pacific.

The protected area, which is already bigger than Greece or North Korea, will almost quadruple in size to 1.5 million sq km, the White House said. That is more than twice the size of France.

Mr Obama will also travel to Midway Atoll, inside the protected area, to underscore the decision.

There he will make the case that climate change "makes protecting our public lands and waters more important than ever", according to the White House.

Papahanaumokuakea is home to a bewildering array of more than 7,000 marine species, including black coral, which can live more than 4,500 years.

The marine protected area is considered federal land where commercial fishing is prohibited.

Mr Obama has made conservation and climate change a central pillar of his presidency - in the face of Republican opposition in Congress - forging international climate accords and promoting national parks.