http://news.bbc.co.uk/2/hi/in_depth/6244496.stmMore than half of the world's population will live in cities by 2008, most of them in developing countries, a report by the UN Population Fund says.
This will add 1.7 billion people to those cities, more than the populations of China and the US combined, it says.
This growth threatens the world with disaster, unless politicians undertake a radical rethink, the report says.
The report, entitled The State of World Population 2007: Unleashing the Potential of Urban Growth, says every week the number of people living in cities in Africa and Asia increases by approximately one million.
And by 2030 the UN Population Fund says the number of city inhabitants will be over five billion, or 60% of world population.
To cope, the UN says, politicians have to stop trying to prevent people moving to cities Urbanisation is inevitable and a good thing, it adds.