The UN secretary general, António Guterres, will attend a Pacific leaders’ summit this week in Tonga with a focus on climate change in the region, one of the world’s most vulnerable to rising sea levels and temperature changes.

The annual meeting of leaders is the top political decision-making body of the region. The week-long summit culminates in the leaders’ retreat, where key decisions are made, which may include an endorsement of a regional policing initiative promoted by Australia. The future for New Caledonia is among other big issues to be addressed at the Pacific Islands Forum (Pif) due to begin in Tonga on Monday.

Australia’s prime minister, Anthony Albanese, and New Zealand’s prime minister, Christopher Luxon – leaders of the forum’s two largest economies – will attend along with most heads of government of the 18-member regional bloc.

As geopolitical tensions rise and competition for influence in the Pacific increases, more outside attention has been focused on some of the smallest countries in the world. The threats posed by climate change and sea level rise will be a central part of the summit, which Guterres will address. Pacific leadership will be looking for more financial support for its climate and disaster initiatives.

“The fate of the Pacific depends on limiting the rise in global temperature to 1.5 degrees Celsius,” the UN secretary general said at a press conference in Samoa on Friday, ahead of the meeting in Tonga.

“This region, the Pacific, contributes 0.02% of global emissions. Yet you are on the frontlines of the climate crisis, dealing with extreme weather events from raging tropical cyclones to record ocean heatwaves.”

The situation in New Caledonia is also likely to be a focus of the meeting, after the French territory was rattled by deadly violence this year over plans from Paris to expand voting rights. This week, a much anticipated high-level visit to New Caledonia by Pacific leaders was postponed, at the request of Louis Mapou, president of the New Caledonia government.

The Cook Islands prime minister, Mark Brown, who is the outgoing Pif chair, said at a recent press conference it is challenging for Pif to navigate the impacts of New Caledonia’s dual status as both a full member of the forum and a territory of France. The unrest has seen the territory added as a “standing item” to the leaders’ agenda which reflects its importance to regional leaders.

In recent years the meeting has drawn increasing interest amid a geopolitical battle for influence in the region between the US and China. As Beijing has expanded its influence in the Pacific and increased its economic and security relationships, the US has boosted its engagement on numerous fronts. Washington has promised more aid, struck security partnerships and opened new embassies. Pacific countries have seen a series of ministerial visits from the US and China, as well as new initiatives across different sectors, and a rise in defence diplomacy.

Fiji’s prime minister, Sitiveni Rabuka, will travel to the Pif on the heels of a visit to Beijing, where he discussed economic development and other ways to deepen ties. The leaders of Vanuatu and Solomon Islands visited China in July.

While Pif members agree on many key priorities, maintaining regional solidarity can be challenging. Last year in Cook Islands, the political divide on deep-sea mining became clear. Since then, Vanuatu has led a charge at the most recent meeting of the International Seabed Authority to prevent licences for exploitation of seabed resources being issued before environmental regulations are in place. Last year, Pacific leaders asked the forum secretariat to convening a regional talanoa (discussion) on this issue. It has yet to take place.