The announcement the US will 're-engage' with the Pacific has been met with both excitement and uncertainty in the region, but may not be an easy win, an expert on international security says.

US vice president Kamala Harris' promised her country would implement stronger policies to increase its involvement in the Pacific, as she spoke by video link to regional leaders at this week's Pacific Islands Forum summit in Suva.

In her virtual address, which has been widely referred to as America's 're-engagement', Harris said the US aimed to establish embassies in Kiribati and Tonga, and would give $60 million to the forum's fisheries agency.

She called for unity against "bad actors".

Massey University security studies senior lecturer Anna Powles said the US overture was a calculated attempt at countering China's growing influence in the region.

"We do have to recognise that the US has a vested interest in re-engaging with the Pacific because of geostrategic competition and because of the concerns about the nature and extent of China's influence in the Pacific," she said.

"[Harris] talks about the international rules based order, and she refers to a 'time when we have bad actors, we must stay united', so clearly there is a message to the Pacific Islands Forum... which is very much about upholding the rules based order."

The US message appeared to receive a positive response; Harris' address was met with applause from leaders at the meeting, and forum chairman and Fijian prime minister Frank Bainimarama immediately commended her.

"I think it's clear to see that the US is certainly looking more like the Pacific partner that we have traditionally held it to be", he said.

"We are very happy we are finally having a US presence in Tonga", Tongan prime minister Siaosi Sovaleni Hu'akavameiliku said.

China fears are 'a non-issue' for many Pacific Island nations

However, if the primary focus of the US re-engagement plan is to counter Chinese influence the situation may not be straightforward.

Many Pacific Island governments have explicitly dismissed notions of Chinese expansionism - some ridiculing it.

In March, Solomon Islands prime minister Manasseh Sogavare said claims that China was planning to build a military base in his country were "insulting".

That same month, Fiji minister of defence Inia Seruiratu declared that: "In Fiji, we are not threatened by geopolitical competition... the single, greatest threat to us is climate change".

Powles said to be effective the US must front on the issues prioritised by Pacific Island governments, including issues that might not fall in line with its own broader foreign policy.

"Strategic competition has become a significant dynamic, but I think something the United States hasn't realise, or perhaps is only beginning to realise, is how much the Pacific itself has changed."

"That's something [they] will really need to be grappling with, those issues of importance in the region, and I'm not just talking about climate change but also issues around self-determination, also long-standing issues such as the anti-nuclear stance."