US-China rivalry and an inter-island rift overshadowed the start of a landmark Pacific summit Tuesday, hampering efforts to focus world attention on the islands' dire climate crisis.

This year's Pacific Islands Forum is the region's most important meeting in years, coming after a Covid-enforced hiatus and as low-lying tropical isles run out of time for climate action.

Fiji president and forum chair Voreqe Bainimarama opened Tuesday’s first meeting with a warning that the "runaway climate change crisis" threatened the security and sovereignty of many Pacific nations.

But instead of a singular focus on the threat of rising sea levels and ever-more-powerful storms, a shock decision by Beijing-allied leaders in Kiribati to quit the forum altogether, revealed on the eve of the summit, loomed over proceedings.

Geopolitical jostling between the United States and China has been building since Solomon Islands controversial signed a security pact with Beijing in April.

United States Vice President Kamala Harris announced Tuesday that she would make an unprecedented video appearance at the summit -- usually restricted to Pacific nations, Australia and New Zealand.

'Fight this emergency'

Leaders gathered at Suva's luxurious Grand Pacific Hotel will discuss a strategy to guide the Pacific through to 2050, keenly focused on the existential threat posed by climate change.

They will also debate announcing a climate emergency in the Pacific and whether to endorse a push, spearheaded by Vanuatu, to ask the International Court of Justice to weigh in on nations' climate obligations.

Vanuatuan prime minister Bob Loughman said Tuesday that the people of the region "are calling on us, Pacific leaders, to take action to fight this emergency".

But Kiribati's exit from the forum has sparked concerns about a fracturing of the Pacific's closely held unity, which gives the region of small island states heft in global climate negotiations.

Tuvaluan foreign minister Simon Kofe told AFP he was "surprised and saddened" by Kiribati's departure, but was optimistic the nation could be enticed to rejoin.

Last year, Kofe made headlines when he addressed the COP summit standing knee-deep in water to draw attention to the threat climate change poses to his low-lying nation, which may disappear below rising seas in the next 50 years.

Faced with such a threat, his priority at the summit is climate change -- Tuvalu will be pushing for a focus on statehood and climate financing.

Concerns about regional security -- brought to the fore by the Solomons-China pact -- "draw a bit of attention away from climate change", Kofe said.

Security versus climate

The summit will be a test of Australia's newly elected Prime Minister Anthony Albanese, who has pledged to do more on climate and to heal his country's fractured relationship with the Pacific.

At the last Pacific Islands Forum leaders' meeting, held in 2019, negotiations descended into shouting and tears as Australia's former government attempted to muzzle leaders who wanted to issue a global call for climate action.

But Albanese also wants to use the summit to raise his concerns about security developments in the region in the wake of the Solomons-China deal.

Speaking to media Tuesday, the leader sought to knit the issues of climate and security together.

"Our neighbours in the Pacific understand that climate change is a national security issue," he told a press conference in Sydney.