A new report projects that two-thirds of the world's population will be living in urban centers and will increase by 2.5 billion in 2050.

According to the United Nations World Urbanization Prospects report, mega-cities worldwide including New Delhi, Tokyo, Mexico City, Sao Paulo and Shanghai will be home to over six billion people in 35 years. The report based its projection on people's preference to live in urban centers and the overall growth rate of the world's population.

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The report said there will be a 66 percent increase in urban dwellers (from 54 percent) by 2050.

Developing countries, especially Asia and Africa, will constitute the majority of the estimated urban population. Of the 2.5 billion, the report said 37 percent comes from China, India and Nigeria with an additional 404 million, 292 million and 212 million additional residents, respectively.

The UN also included challenges these countries would face by 2025. Countries need to plan ahead how they can deliver basic needs and services to urban populations these large.

John Wilmoth, director of the Population Division of the U.S. Department of Economic and Social Affairs, explained at a news conference on Thursday that countries need to plan how they could deliver basic health care, housing, transportation, energy and employment.

For Wilmoth, these services are usually affordable and less environmentally challenging for a denser urban populace.

"The thing to be afraid of is situations in which governments do not plan for the growth that is going to take place. Then you can get sprawls, and slums and cities that are not pleasant places to live," Wilmoth said.

Urban population growth has been increasing since 1990. In the past, there were only 10 mega-cities that have at least 10 million inhabitants. Now, there are 28 of these mega-cities are documented from all over the world.

In Japan, Tokyo currently holds the top spot for being the world's most populous city with 38 million residents. It is followed by New Delhi`s 25 million. Both Shanghai and Mexico City have 23 million urban settlers, while Mumbai and Sao Paulo have 21 million each.

Completing the top 10 most populated urban areas in the world are Osaka with over 20 million, while New York and Cairo both have 18.5 million residents. Osaka and New York are expected to drop to 13th and 14th spots, respectively by 2030 because mega-cities from developing countries are projected to become more prominent.

The report also included a look into the world`s rural population. It reported that rural areas will reach its peak by 2020 and will decline from 3.4 to 3.1 billion by 2050. Asia and Africa, despite urbanizing rapidly, still house almost 90 percent of the rural population worldwide.

Tagsurban, Osaka, Tokyo, Delhi, Cairo, Mexico, 2050