The Pacific Island Forum summit is underway in the Fiji capital, Suva.
In his opening speech, the Fiji prime minister, Laisenia Qarase, has described the meeting as special because it marks the first time that the summit is held at the headquarters of the 16-member organisation.
Mr Qarase says the Forum must promote greater public awareness of its role and speak with a clearer and firmer voice on the critical issues.
He also said the Pacific must express its unrelenting opposition to the polluters and exploiters and be vigilant against those intent on poaching and plundering the Pacific's marine resources.
Earlier, Fiji's president, Ratu Josefa IloIlo, called on island leaders to be more assertive.
President IloIlo has also paid tribute to the founding fathers of the Forum who, he said, were a tower of strength in deepening, promoting and expanding regional co-operation.
Most island leaders are already in Suva but the New Zealand prime minister, Helen Clark, is not due until Thursday night.
She is scheduled to have a bilateral meeting with Mr Qarase, shortly after her arrival.
She is also due to hold talks with her Australian counterpart, John Howard, on Friday, and on Saturday with the Papua New Guinea prime minister, Sir Michael Somare.
Meanwhile, small Pacific states have expressed profound disappointment that the United States has rejected the Kyoto Protocol setting targets for reducing greenhouse gas emissions by 2010.
In a meeting ahead of the Forum, they agreed on a statement expressing their grave concerns and calling for urgent action.
While naming the world's biggest polluter, the US, the leaders were not unanimous on whether to name Australia, which is also opposoed to the Kyoto Protocol.
Tuvalu's prime minister, Saufatu Sopoanga, says he wanted to have Australia named.
The Cook Islands prime minister, Dr Robert Woonton, says if Australia shows an attempt to reduce its emissions then there is a positive reaction to that.
Low-lying countries, such as Kiribati, the Marshall Islands and Tuvalu, are at risk of being wiped out because rising sea levels destroy fresh water supplies and erode scarce land resources.