The world's big cities are already bursting at the seams but are set to grow even larger, with experts predicting that some 70 per cent of the world's population will be urban by 2050.
This will put great strains on infrastructure and the environment, and presents a major challenge to city planners, developers and mayors who gathered here this week at MIPIM, the world's leading annual real estate event, to look for the best way forward.
"The future of the world lies in cities," London's mayor Boris Johnson told a packed auditorium at the opening day of MIPIM Monday.
He was among leaders taking part in a "mayor's think-tank" here, who say they are increasingly starting to work together in looking for urban development initiatives to improve the quality of life for their citizens.
"We have to keep putting the village back into the city because that is fundamentally what human beings want and aspire to," Johnson told the crowd, adapting a famous statement made by India's Mahatma Gandhi that the future of India lay in its 70,000 villages.
"Cities are where people live longer, have better education outcomes, are more productive," Johnson noted, adding that cities are also where people emit less polluting carbon dioxide per capita.
In 1900, around 14 percent of the world's population lived in cities, by 1950 this had risen to 30 percent and today is 50 percent. Currently, there are more than 400 cities with a population over a million, 19 of which have over 10 million inhabitants, Robert Peto, president of the Royal Institution of Chartered Surveyors (RICS), told a conference here.
Much of this surge in the next 40 years will occur in cities in emerging countries such as China, India, Asia, Latin America and Africa, all of which are growing very fast, Tony Lloyd-Jones, Reader in International Planning and Sustainable Development at the University of Westminster in London, told AFP.
A recent study by Citigroup published in Britain's Daily Telegraph newspaper forecast that mega-cities expected to have the fastest growing economies by the middle of the next decade include London, Chicago, Tokyo, New York, Los Angeles and Hong Kong, Sao Paulo, Mexico City, Shanghai, Buenos Aires, Mumbai and Moscow.
"There is a massive explosion of urbanism and this will have a major impact on communities, businesses, economies, and, specifically, our environment," underlined RICS's Peto.
Increased urbanisation, however, also concentrates risks as many big cities are in earthquake and flood zones. And climate change is likely to intensify these risks, Fouad Bendimerad, president of the seismic and megacities initiative in the Philippines, told a MIPIM conference.
Eight to 10 major cities around the world are under continuous threat of earthquake, including Istanbul in Turkey, Bendimerad noted. And it could take considerable time before expertise in building and planning resilient cities is developed, he noted.
Key issues for dense cities over the coming years will include sustainable development, transport and energy use, Lloyd-Jones told AFP.
"Obviously, with the price of oil going up, the pressure is on to conserve fuel and energy," Lloyd-Jones emphasised. This means that cities need to become more efficient in terms of transport infrastructure and investment in public transport is one of the keys to achieving that, he added.
Some cities are already taking steps in this direction, like London, host city for 2012 Olympic Games, which is building new river crossings ahead of that event.
And the city of Melbourne in Australia plans to create denser residential areas along transport corridors, increasing the use of solar power and recycling more onsite.
In Brazil, the city of Curitiba's highly successful program 20 years ago to expand the metropolis along very fast bus routes could also inspire other countries, Lloyd-Jones suggested.
This urban explosion is already having a big impact in China, experts here noted.
Between 18 and 20 million people each year leave the Chinese countryside for its cities, putting great strains on existing accommodation and infrastructure, experts said.
But some of China's fastest-growing cities are now looking abroad for foreign investment to help fund their redevelopment.
Officials from Chongqing, the biggest city in the western China with 32 million population, are exhibiting at MIPIM for the first time to meet potential foreign partners to help fund a massive redevelopment program that aims to double the surface area of the city by 2020.
Canada's second largest city, Montreal, is busy implementing its "Montreal 2025" plan with its numerous huge projects that include the creation of a new science and technology quarter and a huge entertainment district.
The goal is to attract more new residents to the island city, which already boasts 3.9 million inhabitants and attracts 18.8 million visitors every year.
"People want to come back and live in the city centre, which is where it all happens, offers a safe real estate investment where they can feel secure," Richard Deschamps, head of Montreal's 2025 grand plan, told AFP.
Explore further: Scientists warn Obama of marine life harm from seismic tests