Speaking at a United Nations news conference, he said:"Managing urban growth to insure that it is sustainable has become one of the most important development challenges of the current century".
Mumbai, which in 2015 had a population of 19.3 mn will grow by a more modest 41.6% over the two decades to reach 27.3 mn in 2035, just a little bigger than Delhi's current size.
A combination of demographic shifts and overall population growth will result in the more than 2.5 billion people gravitating to urban areas.
The report also estimates that by 2030, the world could have 43 so-called megacities - up from 31 today, according to reports.
As of today, 55 percent of the world population lives in urban areas, increasing to 68 percent by 2050, the report said. By 2020, Tokyo's population is projected to begin to decline, while Delhi is projected to continue growing and to become the most populous city in the world around 2028. The population of Arkhangelsk, Kazan, Krasnoyarsk, Nizhny Novgorod, Novosibirsk, Omsk, Perm, Rostov-on-Don and other cities will either stabilize or slightly grow.
Meanwhile, NAIJ.com reported that the National Population Commission (NPC) had put Nigeria's current population at 198 million people with urban population growing at an average annual growth rate of about 6.5%.
As of 2018, there are 33 megacities and by 2030, 43 megacities are projected, mostly in developing countries.
Currently, India has the largest rural population (893 million), followed by China (578 million).
The report added that understanding the key trends in urbanization likely to unfold over the coming years is crucial to the implementation of the 2030 Agenda for Sustainable Development, including efforts to forge a new framework of urban development.
To ensure that the benefits of urbanization are fully shared and inclusive, policies to manage urban growth need to ensure access to infrastructure and social services for all, focusing on the needs of the urban poor and other vulnerable groups for housing, education, health care, decent work and a safe environment.
"However, the challenge is that in many countries it's taking place so rapidly. and large slum areas have developed that are not maybe achieving the goals of sustainable development the way that we would like".
The News Agency of Nigeria (NAN) reports that DESA in earlier report said: "By 2050, the third most populous country will be Nigeria, which now ranks seventh, and which is poised to replace the United States".