PNG, the South Pacific's most populous nation, will also see a doubling of U.S. development assistance to $32 million, including $25 million to tackle its security priority of climate change, State Department documents submitted to the U.S. Congress show.

Washington is seeking to deter Pacific island nations, which span 40 million kilometres of ocean, from security ties with China, a rising concern amid tensions over Taiwan.

Biden will visit PNG capital Port Moresby on May 22 on his way to a summit of the Quad countries - the United States, Japan, India and Australia - in Sydney, the White House has confirmed. There he will meet 18 Pacific island leaders.

Foreign Minister Justin Tkachenko told Reuters a Defence Cooperation Agreement between the U.S. and PNG was finalised last week, "which now allows us to officially sign it when Biden comes here".

A separate agreement to allow the U.S. Coast Guard to patrol PNG's vast exclusive economic zone, with PNG officials on board as "ship riders", also will be signed and cover satellite surveillance, he said in an interview.

"We will be able to utilise the U.S. satellite security systems. Once we sign that it will help monitor our waters, which we can't at the moment," he said.

"It will be a fantastic agreement protecting our natural resources from being illegally poached and stolen, especially our fishing," he added.

China has a decade-long history of infrastructure projects in the region, and last year struck a security pact with Solomon Islands, which has since placed a moratorium on U.S. Coast Guard vessels entering its waters.

Chinese President Xi Jinping has visited the region three times, including a 2018 visit to PNG, but Beijing last year failed to sign 10 nations to a security and trade deal.

For Biden, the visit also will have personal significance that highlights PNG's importance to regional security.

Two of his uncles were based in PNG in World War Two as airmen, including one who died in a plane crash in May 1944, Biden recalled during a 2016 visit to Australia.

Historians have said PNG was essential to the U.S. drive across the Pacific to liberate the Philippines in the war, and Australian Foreign Minister Penny Wong has urged people to look at history to understand "the strategic importance of Pacific islands to Australia’s security needs".

Classified portions of an Australian defence review were reported by local media to warn Australia would be unable to defend itself from a Chinese missile attack launched from the Pacific.

Chinese anti-ship ballistic missiles, if positioned in the Pacific islands, could stop U.S. and Australian navy movement and interdict vital trade routes, University of NSW professor David Kilcullen, a former special adviser on counterinsurgency to the U.S. Secretary of State, told Reuters.

"A U.S.-China conflict could play out across the whole Pacific including Melanesia and the Polynesian islands, not just in the Taiwan Strait and South China Sea, which puts PNG and the Solomons firmly in the spotlight," he said.

China and the Solomon Islands have denied their security pact allows a navy base.

The U.S. pledged an $800 million economic assistance package after meeting with Pacific island leaders last year, which must be approved by Congress in negotiations not due to progress until the autumn. U.S. embassies recently opened in Solomon Islands and Tonga, but consent for proposed embassies in Vanuatu and Kiribati is yet to be gained, an official told a congressional hearing.

Biden's meeting in person with Pacific leaders is seen in the region as a major step in restoring trust.

U.S. Secretary of State Antony Blinken was told by Pacific leaders in Fiji last year: "We have felt at times, to borrow an American term, like a flyover country.

"Small dots spotted from plane windows of leaders en route to meetings where they spoke about us, rather than with us, if they spoke of us at all."