A new Pacific regional pact calling for aggressive action to combat climate change has achieved a "major accomplishment" by gaining US support, officials said Sunday.

The Majuro Declaration, endorsed by the 15-nation Pacific Islands Forum (PIF) at their summit last week, contains specific pledges on cutting greenhouse gas emissions.

The PIF nations, some of which are barely a metre (three feet) above sea level and risk being swamped by rising waters, have since received wide support led by the United States after presenting the document to more than two dozen countries at a post-forum dialogue.

US Interior Secretary Sally Jewell announced during the session a new climate change fund for Pacific islands vulnerable to rising sea levels.

"Climate change is the defining challenge of our time," she said in launching the Pacific-American fund.

Separately, the US was offering $24 million over five years for projects in "vulnerable coastal communities" in the Pacific, she said.

"It's going to have wide-ranging impacts on every corner of our globe and that's something that we are already seeing, particularly here as I flew into the airport and saw the sandbags from the last time the water inundated the runway."

Marshall Islands minister Tony de Brum said the US support was a "major accomplishment".

"It will serve to convince those who are not convinced yet that it is a good thing to sign on to."

The European Union, Britain, France, Indonesia, South Korea, Thailand and Malaysia also expressed support for the declaration.

"The Majuro declaration is something we very much welcome," British Minister of State Hugo Swire said.

"When you come here and see the highest point on the atoll is the bridge that is about three metres above sea level, that brings it home pretty quickly."

The Majuro Declaration is to be presented to UN Secretary General Ban Ki-moon during the opening of the General Assembly later this month.