Megacities on the rise

As the world's population reaches seven billion, the number of 'megacities' is on the rise as more and more people live in urban areas.

As the world's population reaches seven billion, more and more people are living in urban areas.

More than twenty cities across the world are now classified as 'megacities' -- having populations of more than 10 million. And more than half of the world's megacities are located in Asia.

The Bangladeshi capital Dhaka is one such city, with around 15 million inhabitants. Rapid population growth and extreme poverty is turning the city into a sprawling slum, reports Jeanette Francis.

According to the United Nations Population Fund (UNFPA) the four top megacities currently are Tokyo, Sao Paulo, Mexico City and New York.