India's population is expected to surpass China's in about seven years and Nigeria is projected to overtake the US to become the third most populous country in the world shortly before 2050, a UN report said on Wednesday

United Nations: India's population is expected to surpass China's in about seven years and Nigeria is projected to overtake the US to become the third most populous country in the world shortly before 2050, a UN report said on Wednesday.

The report by the Department of Economic and Social Affairs' Population Division forecasts that the current world population of nearly 7.6 billion will increase to 8.6 billion by 2030, 9.8 billion in 2050 and 11.2 billion in 2100.

It said roughly 83 million people are added to the world's population every year and the upward trend is expected to continue even with a continuing decline in fertility rates, which have fallen steadily since the 1960s.

John Wilmoth, director of the Population Division, said at a news conference that the report includes information on the populations of 233 countries or areas of the world.

"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," he said. "At the other extreme, it is expected that the population of Europe will, in fact, decline somewhat in the coming decades."

The UN agency forecasts that from now through 2050 half the world's population growth will be concentrated in just 10 countries — India, Nigeria, Congo, Pakistan, Ethiopia, Tanzania, United States, Uganda and Indonesia. That order is based on the 10 countries' "expected contribution to total growth", the report said.

During the same period, it added, the populations of 26 African countries are expected to at least double. Nigeria, currently the world's seventh largest country, has the fastest growing population of the 10 most populous countries worldwide, and the report projects it will surpass the US shortly before mid-century.

The new 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, which now has 1.3 billion inhabitants.

The report, titled 'The World Population Prospects: The 2017 Revision', 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 over a lifetime — 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," he said.

The report said birth rates in the 47 least developed countries remain relatively high, with population growth around 2.4 percent a year. While this rate is expected to slow significantly in the coming decades, the UN said the combined population of the 47 countries is projected to increase by 33 percent from roughly 1 billion now to 1.9 billion in 2050.

More and more countries now have fertility rates below the level of roughly 2.1 births per woman needed to replace the current generation, the report said. During the 2010-2015 period, fertility was below the replacement level in 83 countries comprising 46 percent of the world's population, it said.

The 10 most populous countries with low fertility levels are China, United States, Brazil, Russia, Japan, Vietnam, Germany, Iran, Thailand and United Kingdom, the report said.

In addition to slowing population growth, low fertility levels lead to an older population, the report noted. It forecasts that the number of people aged 60 or above will more than double from the current 962 million to 2.1 billion in 2050 and more than triple to 3.1 billion in 2100.

A quarter of Europe's population is already aged 60 or over, and that share is projected to reach 35 percent in 2050 then remain around that level for the rest of the century, the report said.