Like many Pacific islands, the low-lying Marshall Islands are highly vulnerable to climate change and rising seas, which has placed "extreme pressure" on its biodiversity, the World Bank warned in 2021.

It announced Tuesday that it has banned fishing in the waters surrounding two northern isles, an area teeming with vibrant corals, rare giant clams and reclusive deep-sea sharks.

"The only way to continue benefiting from the ocean's treasures is to protect it," Marshall Islands President Hilda Heine said in a statement.

"I am proud of our country's first marine sanctuary, which certainly won't be its last."

The sanctuary lies to the east of Marshall Islands' Bikini Atoll, which the United States bombarded with experimental nuclear bombs throughout the 1940s and 50s.

It covers 48,000 square kilometres (18,500 square miles) -- dwarfing Switzerland -- and surrounds the uninhabited atolls of Bikar and Bokak, which are renowned green turtle nesting grounds.

"We aim to preserve the ecological integrity of this region to ensure that these two atolls remain pristine for future generations," the country's Marine Resources Authority told AFP in a statement.

Conservationist Enric Sala said Marshall Islands was home to some of the healthiest marine ecosystems in the Pacific Ocean.

"This new marine sanctuary protects global biodiversity jewels," said Sala, who founded the National Geographic Pristine Seas expedition that surveyed the atolls in 2023.

"These pristine atolls are time machines that show us what the ocean was like before humans, and what coral reefs could be in the future if we so wish," he told AFP.

The 2023 trip documented "little-known deep-sea communities with potentially new species of fish", a "large abundance of vulnerable species" and "abundant deep-sea sharks".

The Marshall Islands -- population 40,000 -- are a chain of coral atolls and volcanic isles lying between the Philippines and Hawaii.

Its economy relies heavily on fishing.

Non-profit Global Fishing Watch estimates that at least one-third of domestic government revenue comes from tuna alone.

Illegal fishing operations have regularly plundered its waters over the years.

Marshall Islands in 2011 set aside almost two million square kilometres (750,000 square miles) for what it said was the world's largest dedicated shark sanctuary.