China is second with 269 million young people, followed by Indonesia (67 million), the US (65 million) and Pakistan (59 million), Nigeria with 57 million, Brazil with 51 million, and Bangladesh with 48 million, the United Nations Population Fund's (UNFPA) State of the World's Population report said.
It said that developing countries with large youth populations could see their economies soar, provided they invest heavily in young people's education and health and protect their rights.
The report titled 'The power of 1.8 billion', said 28 per cent of India's population is 10 to 24 year-olds, adding that the youth population is growing fastest in the poorest nations. Global number of youths is highest ever.
As the world is home to 1.8 billion young people between the ages of 10 and 24 year, 9 in 10 of the world's young population live in less developed countries.
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"Young people are the innovators, creators, builders and leaders of the future. But they can transform the future only if they have skills, health, decision-making, and real choices in life.
The potential economic gains would be realised through a "demographic dividend", which can occur when a county's working age population is larger than the population that is dependent.
"Never before have there been so many young people. Never again is there likely to be such potential for economic and social progress. How we meet the needs and aspirations of young people will define our common future," the report said.
In order to maximise the dividend, countries must ensure their young working-age populations are equipped to seize opportunities for jobs and other income-earning possibilities, the UN agency said.