The world's current population of 7.6 billion will balloon to 9.8 billion in 2050, with India's numbers to surpass China's in just seven years, a UN report said Wednesday.

Nigeria will overtake the United States by 2050 to become the third most populous country in the world, according to the figures by the UN Department of Economic and Social Affairs.

"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.

At that rate, the global population will reach 8.6 billion in 2030, 9.8 billion in 2050 and 11.2 billion in 2100, it said.

The population of India, which currently ranks as the second most populous country with 1.3 billion inhabitants, will surpass China's 1.4 billion citizens by 2024.

But Nigeria is growing the most rapidly, and the populations in 26 African countries are likely to "at least double" by 2050, according to the report.

The number of persons aged 60 or above is expected to more than double by 2050 and more than triple by 2100.

The aging population is projected to rise from 962 million globally in 2017 to 2.1 billion in 2050 and 3.1 billion in 2100, said the report.