"Africa and Asia are projected to be home to 56 and 64 percent urban population respectively by 2050."
United Nations, July 11 - Delhi, currently the world's second most populous city after Tokyo, is expected to retain the spot till at least 2030, according to a UN report.
According to the Population Division of the UN Department of Economic and Social Affairs, Delhi's population -- presently pegged at 25 million by the UN report -- is projected to reach 36 million by 2030.
The 2014 revision of the World Urbanisation Prospects report, released Thursday, found that the world's largest city is Tokyo with 38 million inhabitants and its population is expected to decline to 37 million by 2030.
Still Tokyo will remain at the top.
Shanghai with 23 million inhabitants retains the third spot.
Mexico City, Mumbai and Sao Paolo, each with 21 million inhabitants, followed by Osaka with just over 20 million people have found place in the top five spots.
The report said that the urban population will grow by 37 percent in India, which currently has the largest rural population.
The urban population will increase rapidly in China and Nigeria as well.
Today, 54 percent of the world's population lives in urban areas, a proportion that is expected to increase to 66 per cent by 2050, the report said.
Africa and Asia remain mostly rural, housing nearly 90 percent of the world's rural population, it said.
Urban areas are on the rise in these two continents, however, at least 40 percent of the population in African and 48 percent in Asia lives in urban areas.
Africa and Asia are projected to be home to 56 and 64 percent urban population respectively by 2050.
It also highlighted the need for a successful urban planning agenda and greater attention to be given to smaller cities where nearly half of all people currently reside.