The world's population will reach 9.7 billion by 2050 as India becomes the largest country, the UN has reported.

In 35 years' time, there will be an extra 2.4 billion people in the world owing to high fertility rates in a handful of countries.

The UN predicts that the figure will rise to 11.2 billion by 2100.

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India is likely to overtake China as the country with the largest population in the world within seven years

Between 2015 and 2050, half of the growth will be concentrated in India, Nigeria, Pakistan, Democratic Republic of the Congo, Ethiopia, United Republic of Tanzania, United States of America, Indonesia and Uganda.

India will surpass China as the country with the greatest population around 2022, and Nigeria is predicted to have more people than the United States by 2050.

The number of people living in 28 African countries is also expected to double, and by 2100 several countries will see a fivefold increase in their population.

Angola, Burundi, Democratic Republic of Congo, Malawi, Mali, Niger, Somalia, Uganda, United Republic of Tanzania and Zambia are all expected to see their populations boom by at least a factor of five.

Children under 15 years currently make up 41 per centof the population in Africa, while those aged between 15 and 24 years account for a further 19 per cent.

This graphic shows how the world population is projected to hit £9.7billion by 2050. The top three largest countries are also forecast to change from China, India and the US in 2015 to India, China and Nigeria in 2050

CHANGING OF THE GUARD: THE TOP FIVE MOST POPULATED COUNTRIES 2015 1. China – 1.4million 2. India – 1.3million 3. USA – 322,000 4. Indonesia – 258,000 5. Brazil – 208,000 2050 1. India – 1.7million 2. China – 1.3million 3. Nigeria – 399,000 4. USA – 389,000 5. Indonesia – 322,000 2100 1. India – 1.7million 2. China – 1.0million 3. Nigeria – 752,000 4. USA – 450,000 5. DR Congo – 389,000 Advertisement

John Wilmoth, director of the population division in the UN's department of economic and social affairs, said that high fertility in some of world's poorest countries could bring problems.

'The concentration of population growth in the poorest countries presents its own set of challenges, making it more difficult to eradicate poverty and inequality, to combat hunger and malnutrition, and to expand educational enrolment and health systems, all of which are crucial to the success of the new sustainable development agenda.'

Fertility, measured by the average number of children that would be born to a woman over her lifetime, is declining across the world but the population continues to rise as rates remain high.

The report also found that the number of people aged over 60 will more than double by 2050 and more than triple by 2100. In Europe, 34 per cent of the population is predicted to be above 60 in the next 35 years because of the declining fertility rate and increase in longevity.

A new UN survey found that China will be overtaken by India, while Nigeria will overtake the United States

WORLD POPULATION GROWTH 2015: 7.3billion 2050: 9.7billion 2100: 11.2billion Advertisement

Life expectancy at birth was also shown to have increased significantly in the least developed countries - from 56 years in 2000-2005 to 62 years in 2010-2015. The rise is more than double that of the rest of the world.

Wu Hongbo, UN under-secretary-general for economic and social affairs, explained the importance of the report.

She said: 'Understanding the demographic changes that are likely to unfold over the coming years, as well as the challenges and opportunities that they present for achieving sustainable development, is key to the design and implementation of the new development agenda.'

The findings, released in the United Nations' Time for Global Action for People and Planet report, were calculated from the 2010 round of national population censuses and recent demographic and health surveys.

Janet Morrison, chief executive of Independent Age, the older people's charity, said: 'This upturn in longevity is to be applauded, as people are largely living healthier lives for longer.

'However, as a society we need to make greater preparations to meet the needs of a rapidly ageing population.

'The current health and social care systems are under great strain and this is likely to get worse unless we have an honest debate about what kind of old age we want and how much we are prepared to pay for it.'

Simon Ross of Population Matters added: 'The world’s population is rising at an alarming rate. These UN projections should act as a further warning that we should not ignore this issue.