The world's population is projected to rise to 9.7 billion in 2050 from the current level of 7.1 billion.
And India will overtake China as the world's most populous nation, according to a French study.
A bi-annual report by the French Institute of Demographic Studies (Ined) has projected there will be 10 to 11 billion people on the planet by the end of the century.
The projections run parallel to forecasts by the UN, the World Bank and other prominent national institutes.
A UN study in June said the global population would swell to 9.6 billion in 2050 and the number of people aged 60 and above would catapult from 841 million now to two billion in 2050 and nearly three billion in 2100.
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Ined says Africa will be home to a quarter of the world's population in 2050 with 2.5 billion people, more than double the current level of 1.1 billion.
Gilles Pison, the author of the report, said the prevailing fertility rate in Africa was around 4.8 children per woman - far higher than the global average of 2.5.
The Americas will breach the one-billion mark in 2050 with 1.2 billion inhabitants against 958 million at present.
And Asia's population will increase from 4.3 billion to 5.2 billion in 2050, Ined forecast.
The world's most populous nations are currently China with 1.3 billion people; followed by India (1.2 billion); the US (316.2 million); Indonesia (248.5 million) and Brazil (195.5 million).
But in 2050, India will take pole position with 1.6 billion people.
China will be in second place at 1.3 billion.
Nigeria, Africa's most populous country, will outstrip the US with a population of 444 million against a projected 400 million Americans in the middle of the century.
