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Kiribati's President, Anote Tong, says his country may already be doomed by global warming - and he wants New Zealand and Australia to consider the issue of environmental refugees.

"We may already be at the point of no return, where the emissions in the atmosphere will carry on contributing to climate change, so in time our small low-lying islands will be submerged," Mr Tong said yesterday in Wellington.

Kiribati's highest point of land is just 2m above sea level, and under "worst-case" scenarios it will be flooded by the Pacific this century and its 94,000 people will have to be re-settled in other countries.

Mr Tong, a graduate of the London School of Economics, said climate change "is not an issue of economic development, it's an issue of human survival".

He told a press conference marking World Environment Day, which Wellington hosted for the United Nations, that changes were obvious in his country: "Things are happening we did not experience in the past.

"We may be beyond redemption, we may be at the point of no return where the emissions in the atmosphere will carry on to contribute to climate change to produce a sea-level change that in time our small low-lying islands will be submerged.

"Villages that have been there over the decades, maybe a century, and now they have to be relocated. Where they have been living over the past few decades is no longer there, it is being eroded."

UN Environment Programme executive director Achim Steiner - also in Wellington for a closely packed itinerary - said it was difficult for island nations to watch as the effects of climate change took hold.

"It's a humbling prospect when a nation has to begin talking about its own demise, not because of some inevitable natural disaster ... but because of what we are doing on this planet," Mr Steiner said.

The world must find the "collective purpose" to combat climate change, and everyone on the planet must take their responsibility seriously, he said.

Kiribati is made up of 33 coral atolls in three main groups.

"Every second week when we get the high tides, there's always reports of erosion," Mr Tong said. The rising sea was contaminating the water aquifer and time was running out.

"To plan for the day when you no longer have a country is indeed painful but I think we have to do that."

Prime Minister Helen Clark told the ABC there was already a small community from Kiribati in New Zealand: "If the worst happens no doubt they would be bigger".

Mr Tong said the worst possible scenario meant his country had 50 or 60 years: "I think we have to [leave], in fact I've appealed to the international community that we need to address this challenge.

"It's a challenge, I think not for any one single country but I think for the whole global community.

"Maybe we have a few decades to address this but we believe that we should begin to address the issue yesterday."

Mr Tong said New Zealand offered opportunity, "but I think from our own perspective ... it is important that if our people were to relocate, they should do so as trained, skilled people rather than people coming here and adding to the problems, their own problems and to the national problems".

Planning for migration needed to start now to find a new home and a new future for the people of Kiribati.