Major cities in the world including Mumbai and Kolkata are witnessing a rare phenomenon as the number of people who are moving out of these metros are on an increase, contrary to what has been predicted.
A UN report said these cities have far greater number of people moving out and few of these cities will be of the size that doomsayers had predicted for them in the 1970s.
Even though by next year, more than half of the world population will be living in urban areas, the urban growth is showing a decline in most regions, the United Nations Population Fund (UNFPA) said.
Population of towns and cities in developing countries like India is set to double in the space of a generation, while urban population in developed world is expected to grow relatively lower, the 'State of the World Population 2007' report that was released on Wednesday said.
In comparison to the urban population growth rate, the world's rural population is expected to decrease by some 28 million between 2005 and 2030.
Mega cities are still dominant but they have not grown to the sizes once projected and has consistently declined in most world regions says, the report said.
Pointing out that large cities like Kolkata or Seoul have more people moving out than in, the report says few are close to the size that doomsayers had predicted for them in the 1970's.
Among the 20 mega cities, the population of only six grew at rates consistently above 3 per cent a year over the last 30 years. The others experienced mainly moderate or low growth, it said.