London, Mar. 12: Nine nations -- India, Pakistan, Nigeria, Ethiopia, the US, Congo, Tanzania, China and Bangladesh will be majority contributors to the world’s population that will hit seven billion by the early part of 2012 and will top nine billion in 2050, according to a UN estimate.

Hania Zlotnik, director of the UN Population Division, said: ``There have been no big changes'''' from the previous estimate in 2006. We are still projecting that by 2050, the population of the world will be around 9.1 billion."

"The projections are based on the assumption that fertility that is now around 2.56 children per woman is going to decline to about 2.02 children per woman in the world," she added.

Zlotnik said if fertility remained about where it is now, then world population would reach 10.5 billion by 2050. If fertility fell even more than expected, to about 1.5, then the population would only increase to eight billion by mid-century, she said.

Population growth will remain concentrated in the most populous countries through 2050.

In sharp contrast, the populations of 45 countries or regions are expected to decline at least 10 per cent over the same period, including Japan, Italy and many other countries that were once part of the Soviet Union, the UN said.

According to the study, the largest number of migrants will head to the United States - an estimated 1.1 million every year between 2010 and 2050.

The immigrants and the US birth rate will help boost the US population from an estimated 314.7 million in mid-2009 to 403.9 million in 2050, according to Gerhard Heilig, chief of the UN''s Population Estimates and Projections Section. (ANI)