By 2025 10.3 percent of the world 's urban population will live in megacities says the UN . The most populous city is Tokyo in Japan , with 100 million inhabitants . New Delhi , for example , is projected to have 29.49 million inhabitants by 2025 , according to Demographia -- up from 20.99 million in 2010 . Megacities in countries like India and China will grow fastest over the next 15 years .
By 2025 10.3 percent of the world 's urban population will live in megacities says the UN . The most populous city is Tokyo in Japan , with 100 million inhabitants . Megacities in countries like India and China will grow fastest over the next 15 years .