On a visit to Samoa, he said the fate of Pacific islands depended on limiting global warming to 1.5 degrees Celsius above pre-industrial levels.

Nearly 200 nations agreed to strive for that target in the 2015 Paris climate agreement, but UN estimates indicate that the world is not on track to achieve it.

"High and rising sea levels pose an enormous threat to Samoa, to the Pacific and to other small island developing states, and these challenges demand resolute international action," Guterres said.

The Pacific region contributes just 0.02 percent of global carbon emissions, he noted.

"Yet you are on the front lines of the climate crisis, dealing with extreme weather events from raging tropical cyclones to record ocean heatwaves," the UN secretary-general continued.

"Sea levels are rising even faster than the global average, posing an existential threat to millions of Pacific Islanders," he added.

"People are suffering. Economies are being shattered. And entire territories face annihilation."

Guterres urged richer nations to live up to their commitments to help pay for the consequences of climate change in developing countries.

He also called for international action to tackle the impact of climate change, overfishing and plastic pollution on the Pacific Ocean.

Guterres said major powers' interest in the region was rising, an allusion to the jostling for power and influence in the Pacific between China and the United States and its allies.

"The Pacific is best managed by Pacific islanders," the UN chief said. "It must never become a forum for geostrategic competition."