Japan on Tuesday welcomed Pacific island leaders for a three-day summit on issues from rising sea levels to security as Western countries vie with China for influence in the region.

Prime Minister Fumio Kishida is also expected to seek to soothe concerns about the ongoing release of treated wastewater from Japan's crippled Fukushima nuclear plant into the Pacific.

Kishida said ahead of the 10th triennial PALM summit that Japan and the participants "have worked hand in hand to tackle common challenges such as climate change and disaster management".

"As we adapt to changing circumstances... Japan will continue to stride forward together with Pacific island countries and regions," he wrote in a Japan Times article published Monday.

A joint statement is due Thursday from the summit, which brings together Japan and representatives from the 18 Pacific Islands Forum (PIF) members including Australia and New Zealand, whose prime ministers will not attend.

With US support, Japan has strengthened defence cooperation in the hotly contested Pacific region where China is also offering aid for infrastructure and security.

China notably signed a secretive security pact with Solomon Islands in 2022, sparking fears it could one day use the island to gain a strategic military toehold in the region despite assurances from Beijing and Honiara.

In January, PIF member Nauru cut ties with Taiwan in favour of China -- leaving only 12 states worldwide that recognise Taipei diplomatically, including Palau, another PIF member.

Palau's national security coordinator Jennifer Anson told Japanese broadcaster NHK that many in the group were averse to saying "anything bad about China" because of their close ties.

She also expressed hope for Japanese support in maritime surveillance to track Chinese research vessels in Palau's exclusive economic zone, according to NHK.

Ships carrying vital energy imports to Japan pass through the waterways surrounding the PIF members, which are also important fishing zones for Japan.

Tokyo is expected to promise assistance to the islands in a range of fields from maritime security to healthcare, education and adapting to climate risks.

But the government is also seeking understanding on the thorny issue of the release of treated wastewater from the Fukushima plant, which went into meltdown after a 2011 tsunami.

In November, PIF leaders issued a joint statement of "strong concerns" about the release, endorsed by the UN's nuclear energy agency, but Japan is keen for it not to undermine its relations with the group.

Top government spokesman Yoshimasa Hayashi told reporters on Tuesday the summit was an opportunity to "reassure them through thorough explanations based on science".