The United States on Thursday announced the creation of the world's largest marine sanctuary in the Pacific, where commercial fishing and energy exploration are off limits.

The move expands the already existing Pacific Remote Islands Marine National Monument -- west of Hawaii and northeast of Australia -- to six times its previous size.

"We're talking about an area of ocean that's nearly twice the size of Texas, and that will be protected in perpetuity from commercial fishing and other resource-extraction activities, like deep-water mining," said Secretary of State John Kerry.

Former president George W. Bush declared the area a national monument in 2009, and an executive order from President Barack Obama makes the protected space even larger.

The total protected area now includes 490,000 square miles (1.27 million square kilometers) around the Wake and Jarvis Islands and Johnston Atoll.

"This is the grand-daddy of all marine protected areas around the world," said Jackie Savitz, vice president for US oceans at the advocacy group Oceana.

"Some of these areas had like a 50-mile radius around them, now they are going to have a 200-mile radius."

A key goal is to protect the undersea mountains that provide habitat and hunting grounds for tuna, sea turtles, manta rays, and sharks, and to allow them to breed and multiply.

The area "is also home to millions of seabirds that forage over hundreds of miles and bring food back to their rookeries on the islands and atolls," the White House said in a statement.

Coral reefs that are in peril from bleaching and ocean acidification are plentiful in the area, and protecting them allows scientists to use them as a benchmark for global research on climate change.

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

However, some recreational fishing will continue to be allowed, with special permits.

Biologists at the US Fish and Wildlife Service say the establishment of the protected area has already helped boost some creatures that had all but disappeared at Johnson Atoll.

They include "Great Frigatebirds, Sooty Terns, Red-tailed Tropicbirds, and other species that are known to feed as much as 300 to 600 miles offshore," the statement said.

Also two kinds of albatross that forage across the North Pacific have "recently recolonized Wake Atoll, making it one of the few northern albatross colonies outside of the Hawaiian archipelago," it added.

Obama first announced plans to expand the marine reserve in June at a two-day conference on the world's oceans, hosted by the State Department.

With just one to three percent of the world's oceans currently under protection, Kerry called on global powers to take more steps to end overfishing and protect global fish stocks.

"There's just too much money chasing too few fish."