Many low-lying coral islands in the South Pacific, long thought to be in danger of being swamped by rising sea levels, have managed to keep their size stable and even grow, new research shows.

Two researchers used old aerial photos and more modern satellite photos to track changes in the land mass of 27 islands over the last 60 years.

This artist's drawing, based on an undated satellite photo provided by Auckland University, shows an island of the Funafuti Atoll of Tuvalu in the South Pacific. The dotted lines indicate the coastlines in 1984 while the solid line represents the coastlines as of 2004. (Auckland University/Associated Press)

They found that while four of the islands had shrunk in size, the other 23 had either maintained their size or grown. All this took place while the local sea levels rose by 12 centimetres over the six decades.

It appears that many of the islands changed along with climate patterns, as deposits of coral debris and sediment built up on their shores.

The scientists say assumptions that the islands would "sit there and drown" as sea levels rise need to be reworked.

"They're not all growing, they're changing," said Paul Kench of the University of Auckland and one of the authors of the study. "They've always changed … but the consistency [with which] some of them have grown is a little surprising," he told The Associated Press.

Seven of the nine islands in the coral island group of Tuvalu, for instance, grew by an average of more than three per cent over the last 60 years, researchers found. A cyclone almost 40 years ago helped to deposit a huge amount of sediment on two of the islands. The highest point of elevation in Tuvalu is just 4.5 metres above sea level.

The change was even more dramatic on the three main islands of Kiribati, where the president warned just two years ago that his island nation would be swamped by the sea within 100 years.

One island "grew" by 30 per cent, while the other two added 16.3 per cent and 12.5 per cent more land mass.

Kiribati and other islands in the area appear to be adjusting to rising sea levels by slowly migrating across their reef platforms, adding sand and gravel from coral reefs that encircle the islands.

So does this mean that residents of all low-lying atolls can relax? Not necessarily. If sea levels pick up the speed of their rise, the islands face the possibility of "a very rapid rate of island destruction," Kench said.

But if that doesn't happen, the scientists say residents of the low-lying islands may not need to leave after all.

The research is published in the scientific journal Global and Planetary Change.

With files from The Associated Press