UNITED NATIONS (AFP) - The world population is projected to top nine billion in 2050, up from 6.8 billion this year and seven billion early in 2012, according to UN estimates released Wednesday. Most of the additional 2.3 billion people will swell the population of the developing world, estimated to soar from 5.6b this year to 7.9b in 2050, and to spread among the 15-59 age group (1.2b) and those 60 or over (1.1b), the data showed. The 2008 Revision of the official UN population projections forecast minimal change in the population of the more developed nations, which should rise from 1.23b to 1.28b during the same period. That population would have in fact dipped to 1.15b without the projected net migration from developing to developed countries, expected to average 2.4m persons annually from 2009 to 2050, it noted. In 2005-2010, net migration in eight countries or areas more than doubled the contribution of natural increase (births minus deaths) to population growth: Belgium, Macau, Czech Republic, Luxembourg, Qatar, Singapore, Slovenia and Spain. During the 2010-2050 period, major net receivers of foreign migrants are projected to be the United States (1.1 million annually), Canada (214,000), Britain (174,000), Spain (170,000), Italy (159,000), Germany (110,000) Australia (100,000) and France (100,000). Major countries of net emigration are expected to be Mexico (334,000 annually), China (309,000), India (253,000), the Philippines (175,000) and Pakistan (161,000). The population of the 49 least developed nations is meanwhile slated to double from 0.84 billion this year to 1.7b in 2050. Growth in the rest of the developing world is estimated to be robust, but less rapid, with its population increasing from 4.8b to 6.2b between now and 2050. Future growth would depend on the future direction of fertility rates, with fertility declines from 2.56 children per woman in 2005-2010 to 2.02 children per woman in 2045-2050, according to the most probable scenario. "This report is a timely warning to world leaders of the long-term consequences of failing to invest in the needs of about 200 million women who lack access to safe and effective contraceptives," said Thoraya Ahmed Obaid, the executive director of UNFPA (UN Population Fund). The data, prepared by the Population Division of the UN Department of Economic and Social Affairs, however show that slowing population growth resulting from reductions in fertility leads to population aging. In the more developed countries, 22 per cent of people are already 60 and over and that proportion is expected to reach 33pc in 2050. By then, the number of older persons in the developed world is expected to be more than twice that of children. By contrast, just nine percent of the population of developing countries today is aged 60 or over but the proportion will more than double by 2050 to reach 20pc. The UN study incorporates findings of the most up-to-date national population censuses and of several specialized population surveys conducted around the world.