The world's population of 7.6 billion will balloon to 9.8 billion by 2050 and India will overtake China as the most populous country in just seven years, a United Nations report has said.
The report, released by the UN Department of Economic and Social Affairs on Wednesday, forecasts that from now to 2050, half of the world's population growth will be concentrated in just nine countries: India, Nigeria, Congo, Pakistan, Ethiopia, Tanzania, the US, Uganda and Indonesia.
Those nations are listed in the order of their "expected contribution to total growth".
At that rate, the world's population will reach 8.6 billion in 2030, 9.8 billion in 2050 and 11.2 billion in 2100, the report titled The World Population Prospects: The 2017 Revision said.
By 2050, Nigeria will overtake the US to become the third most populous country.
"With roughly 83 million people being added to the world's population every year, the upward trend in population size is expected to continue, even assuming that fertility levels will continue to decline," the report's authors said.
"The population in Africa is notable for its rapid rate of growth, and it is anticipated that over half of global population growth between now and 2050 will take place in that region," John Wilmoth, director of the Population Division, said at a news conference.
"At the other extreme, it is expected that the population of Europe will, in fact, decline somewhat in the coming decades."
The projections also forecast that China, which currently has 1.4 billion inhabitants, will be replaced as the world's most populous country around 2024 by India with a current population of 1.3 billion.
Nigeria, currently the world's seventh largest country, is growing the most rapidly, and the populations in 26 African countries are likely to "at least double" by 2050.
The report also said fertility has been declining in nearly all regions in recent years.
Between 2010 and 2015, Wilmoth said "the world's women had 2.5 births per woman ... but this number varies widely around the world".
"Europe has the lowest fertility level, estimated at 1.6 births per woman in the most recent period, while Africa has the highest fertility, with around 4.7 births per woman," said Wilmoth.
In addition to slowing population growth, low fertility levels lead to an older population, the report noted.
The number of persons aged 60 or above is expected to more than double by 2050 and more than triple by 2100.