The report 'World Population Prospects' says the world's population will hit 7.2 billion next month and is projected to reach 10.9 billion by 2100, with the growth mainly occurring in developing countries, with more than half in Africa.
But, with the number of future global dwellers linked to fertility, the number at the end of the century could be as high 16.6 billion or even fall to 6.8 billion, it adds.
The report says India is expected to become the world's most populous country, passing China around 2028, when both countries will have populations of 1.45 billion.
After that, India's population will continue to grow and that of China is expected to start decreasing.
"Although population growth has slowed for the world as a whole, this report reminds us that some developing countries, especially in Africa, are still growing rapidly," Wu Hongbo, the Under-Secretary-General for Economic and Social Affairs, said while releasing the report.
The report notes that the population of developed regions will remain largely unchanged at around 1.3 billion from now until 2050. In contrast, the 49 least developed countries are projected to double in size from around 900 million people in 2013 to 1.8 billion in 2050. Nigeria's population is expected to surpass that of the United States before 2050.
"While there has been a rapid fall in the average number of children per woman in large developing countries such as China, India, Indonesia, Iran, Brazil and South Africa's rapid growth is expected to continue over the next few decades in countries with high levels of fertility such as Nigeria, Niger, the Democratic Republic of the Congo, Ethiopia and Uganda but also Afghanistan and Timor-Leste, where there are more than five children per woman," said John Wilmoth, the Director of the Population Division in the UN's Department of Economic and Social Affairs.
Overall, life expectancy is projected to increase in developed and developing countries in future years. At the global level, it is projected to reach 76 years in the period 2045-2050 and 82 years in 2095-2100.
The report's figures are based on a comprehensive review of available demographic data from 233 countries and areas around the world, including the 2010 round of population censuses.