WASHINGTON (Reuters) - President Barack Obama on Thursday will designate the largest marine sanctuary in the world in an area of the Pacific Ocean that will be off-limits to commercial fishing and deep-sea mining, the White House said on Wednesday.

Obama will sign a proclamation that increases the size of the Pacific Remote Islands Marine National Monument by six-fold to 490,000 square miles (1.27 million sq km/370,000 sq nautical miles).

The White House said in a statement the area is "of particular interest because science has shown that large marine protected areas can help rebuild biodiversity, support fish populations, and improve overall ecosystem resilience."

The coral reefs and marine ecosystems of this section of the south-central Pacific are some of the most vulnerable areas to climate change and ocean acidification, the White House said.

Commercial fishing and other resource extraction activities, such as deep-sea mining, are banned in the protected area. But the White House said recreational and traditional fishing that are consistent with the conservation goals of the monument will continue to be allowed in the expanded area.

(Reporting by Eric Beech; Editing by Sandra Maler)