"Settlements in coastal lowlands are especially vulnerable to risks resulting from climate change, yet these lowlands are densely settled and growing rapidly," the researchers in the United States and Britain said in the article.

Based on new computer population models and NASA satellite data, it estimated that 634 million people lived in the coastal zone in 2000, including 360 million in towns and cities.

More than 75 percent were in Asia. Globalisation is promoting a shift towards coasts in countries including China and India by fostering a world trade largely dependent on shipping.

RISING SEAS

UN climate experts projected last month that sea levels could gain by 18 to 59 cms (7.1 to 23.2 inches) by 2100, and keep rising for centuries. They also forecast shifts including more powerful storms,droughts and heatwaves because of emissions of greenhouse gases, mainly from burning fossil fuels.

Wednesday's report said even people living up to 10 metres above sea level could be vulnerable to cyclones, subsidence, erosion of river deltas or intrusion of salty sea water onto cropland.

"If you are in that zone you need to take the issues of sea level rise seriously," said Gordon McGranahan, lead author at the London-based International Institute for the Environment and Development.

Ranked by population, China is most at risk with 143 million people living by the coast, followed by India, Bangladesh, Vietnam, Indonesia, Japan, Egypt and the United States.

By another measure, small island states will be hardest hit. More than 90 percent of the Maldives, the Marshall Islands, Tuvalu, the Cayman Islands and the Turk and Caicos Islands are less than 10 metres above sea level.

"Relatively small shifts in settlement location, out of a coastal plain onto more elevated ground, can make a major difference," according to the authors, also from the City University of New York and US Columbia University.