King Charles would be making his first-ever speech to the Commonwealth grouping in his capacity as the head when the Commonwealth Heads of Government Meeting takes place in October.

Samoa will be the venue for this historic event after missing the annual Commonwealth Day event to recover from cancer treatment in March.

King Charles has cut short his tour of Australia by six days and cut out New Zealand completely from his October itinerary but Samoa remains on the list.

The last time a British monarch visited Samoa was 1977, when the late Queen Elizabeth came for a day tour.

Climate change and efforts to keep up with advances in artificial intelligence top the agenda the CHOGM.

The Commonwealth is a voluntary club of 56 nations headed by King Charles, having evolved out of the British empire and spanning 2.5 billion people, with 11 Pacific nations among its members.

"This is not a threat about extinction tomorrow, many of them are thinking, it is extinction today," Commonwealth secretary general Patricia Scotland said of the climate change risks that make small Pacific nations particularly vulnerable.

"If we look at what's happened in countries like Vanuatu and Nauru and all of them, they see this rise in sea level and the rise in temperature as an imminent threat."

Samoa will be the first Pacific small island state to host the annual Commonwealth Heads of Government meeting, putting the spotlight on climate change.

The grouping wanted to put climate finance advisers in member nations to boost fund-raising efforts to tackle the fallout of climate change, Scotland said.

Other topics for discussion are artificial intelligence and digitalisation of the global economy.

"If the small and developing states are left behind, then their opportunity to take advantage of that huge potential increase in development and opportunity is going to be gone," she added.