Alongside its 18 member states including key players Australia and New Zealand, gatherings of the Pacific Islands Forum are typically attended by dozens more countries as observers or dialogue partners.

But this year's host, close China ally the Solomon Islands, has barred most of those partners from attending -- sparking accusations that Honiara was working at Beijing's behest to exclude long-time participant Taiwan.

The move prompted condemnation from fellow Pacific nations, of which three -- Marshall Islands, Palau, Tuvalu -- still recognise Taipei.

China counts the Solomon Islands among its closest partners and backers in the South Pacific.

The two signed a secretive security pact in 2022 and Beijing even donated police vehicles and equipment ahead of the forum.

A welcoming ceremony for leaders in the Solomons capital of Honiara on Monday took place at the National Stadium, a 10,000-seat arena built and financed by the Chinese government.

Formal meetings will kick off on Wednesday and primarily take place behind closed doors.

Also attending will be Australian leader Anthony Albanese, who was in neighbouring Vanuatu on Tuesday to discuss a deal aimed at deepening Canberra's links to the Pacific nation.

But speaking alongside Albanese, Prime Minister Jotham Napat said there were concerns that the wording of the deal would limit the country's ability to access funds for "critical infrastructure" from other nations.

The pact -- known as the Nakamal Agreement -- has been seen as a response to China's increased presence in the country.

- 'Outsiders' meddling -

Observers warn a split at Wednesday's forum over the China issue could undermine essential regional cooperation on everything from climate change to health, security and transnational crime.

New Zealand's top diplomat Winston Peters told AFP last month it was "obvious" that outside forces were meddling in the summit.

"Outsiders are now telling us who we can have as guests. That's not the Pacific way," he said.

Peters, Australian Foreign Minister Penny Wong and other officials have warned the banning of dialogue partners could have an impact on aid being provided to the Pacific.

Communist China has never ruled Taiwan, but Beijing insists the island is part of its territory and has threatened to use force to bring it under its control.

China bristles at any official diplomatic recognition of the democratic island.

The two have long vied for influence in the South Pacific, with Beijing spending hundreds of millions of dollars building sports stadiums, presidential palaces, hospitals and roads across the region.

Mihai Sora, who heads the Pacific Islands Program at the Lowy Institute, told AFP that China had become the "elephant in the room".

"China is effectively shaping the Pacific Islands Forum leaders meeting, and it's not actually a member of the Pacific Islands Forum," said the former Australian diplomat.

- Touchy talks -

On Thursday, participants will head to the picturesque seaside settlement of Munda, over 300 kilometres (about 190 miles) from the capital, for a "leaders retreat".

But there may be little they can agree on.

Beyond China, key issues causing friction include a review of the forum's regional architecture, which will decide who can participate.

So too is cooperation in transnational security, with member states reluctant to relinquish what they see as hard-fought sovereignty to help combat regional problems.

Climate change is also a major talking point on the back of Vanuatu's win in the International Court of Justice, which declared states are obliged to tackle the issue and reparations could be awarded if they didn't.

The Forum partners work together on disaster risk management and climate finance, but there is disquiet in some quarters over individual nations opening up for deep sea mining or oil and gas exploration.

Beijing's top diplomat in the Solomons, Cai Weiming, has said the China Police Liaison Team -- deployed as part of the two nations' security pact -- could assist in security for the summit.

And Beijing has also signalled that it will be present at the summit in some form or another.

New Zealand officials told AFP they feared the forum will "fall apart" if that happens.