The Pacific island nation is strategically located close to trade routes to Australia and Japan, in a region where Washington and New Delhi are concerned about China trying to woo tiny nations with diplomatic and financial incentives.

US Secretary of State Antony Blinken will follow Indian Prime Minister Narendra Modi in holding separate talks with 14 Pacific leaders including New Zealand Prime Minister Chris Hipkins who have gathered in the PNG capital Port Moresby.

Before that meeting, Blinken is expected to sign a defence cooperation agreement with Papua New Guinea Prime Minister James Marape that will give US troops access to the Pacific nation's ports and airports.

The State Department said the pact would "enhance security cooperation and further strengthen our bilateral relationship, improve the capacity of the PNG Defence Force, and increase stability and security in the region".

Marape last week said the deal would offer Washington movement in the country's waters in return for access to US satellite surveillance to battle "illegal activities on the high sea".

Blinken replaced Joe Biden at the summit after the US president cancelled the trip to take part in debt ceiling talks in Washington.

Biden -- whose uncle died in Papua New Guinea during World War II -- would have been the first sitting US president to visit the island nation.

- No longer a 'sleepy outpost' -

Washington is courting Pacific nations more intensely after Solomon Islands became the unlikely epicentre of a US-China diplomatic tussle last year when it signed a security pact with Beijing.

The US defence pact is being framed as a deal to protect Papua New Guinea's territorial borders but experts say China's Pacific presence is a key driver.

"Port Moresby is no longer the sleepy diplomatic outpost it once was," said Gordon Peake, a senior adviser for the Pacific Islands at the United States Institute of Peace.

"While China might not be mentioned anywhere in the document, it's an important subtext in this story of deepening US-PNG relations."

Marape said the deal would not prevent him from signing similar deals with other nations, including China.

Modi's talks earlier in the day with Pacific leaders are expected to focus on trade, development and climate change.