The United Nations has forecast that India, China, Nigeria, Indonesia and the United States will face big challenge in the next four decades, as these countries are set to lead the world's growth in urban populations.

Businessmen at the Peak look at high-rise residential and commercial towers in Hongkong.

According to United Nations 2011 Revision of the World Urbanization Prospects, the projected increase in urban population in the next four decades (2010 to 2050) is huge in Africa and Asia.

In the next four decades, India is expected to add 497 million to its urban population, China - 341 million, Nigeria - 200 million, the United States - 103 million and Indonesia - 92 million.

"Cities are where the pressures of migration, globalization, economic development, social inequality, environmental pollution and climate change are most directly felt," the United Nations said in a statement. "Yet, at the same time, they are engines of the world economy and centers of innovation where many solutions to global problems are being piloted," it added.

The UN has released World Urbanization Prospects ahead of Rio+20 - The United Nations Conference on the Sustainable Development in June in a bid to urge the world leaders to come up with plans to meet the challenges like providing urban jobs, housing, energy and infrastructure to dealing with urban poverty, expansion of slums and a deterioration of the urban environment, as the world's urban population is expected to shoot up by 2050.

"About one third of the world urban population lives in slum conditions. The launch of the World Urbanization Prospects is very timely as the world gathers together to promote sustainable development for the future we want. We expect world leaders to come up with concrete action plans to realize sustainable cities," said Sha Zukang, Secretary General of Rio+20.