The number of people living in slums will double to two billion by 2030 if urgent action is not taken, the third World Urban Forum in Vancouver, Canada, has been told.
By Ben Sutherland
BBC News website in Vancouver
The figure was given by Inga Bjork-Klevby, the Assistant Secretary General of the United Nations, in a special session in which members of parliaments around the world discussed the problems facing their cities.
Activists argue the world is ignoring global standards on the right to a home
There are currently one billion slum dwellers, but soaring urbanisation will be behind the increase if it is not managed properly, Ms Bjork-Klveby said.
"Some have chosen to ignore or even destroy these settlements," she said.
"We need a common vision for reducing the burgeoning poverty in cities."
The rapid growth in urbanisation is the main focus of the forum, with the number of urban dwellers forecast to reach a total of five billion by 2030 - out of a total population of 8.1 billion.
Next year, for the first time in human history, more than half the world's population is expected to be living in urban areas.
Senator Rodolfo Biazon of the Philippines said that in his country, as in many others in the developing world, one of the reasons for the surge in slum dwellers was that increased globalisation has meant farmers are now no longer able to make a living from the land.
"Many developing countries' farmers are defeated by the farmers of the developed world, causing these farmers to flock to the city to find a job,"
"But there they find that our industries are also in unfair competition with the developed world, which leads to a growth in the slums."
Mr Biazon added that increased urbanisation is already taking its toll in the Philippines' capital Manila, where the exploding population means water is needed from rivers 100km away.
The Philippines' government has been trying to put together a "safety net"
package for farmers as one of the ways to try and control migration, he added.
This was one of a number of strategies discussed by the MPs.
In South Africa, government negotiations with banks have seen 42 billion Rand set aside to help with construction, while Morocco's senate has pressurised banks into reducing their housing interest to 5%.
Indeed, in many cases banks were seen as the key to reducing slum dwelling, by providing the means for people to buy their own homes.
"We've got to become very creative," said Hilson Baptiste, the housing minister for Antigua and Barbuda, who has persuaded banks to extend their maximum mortgage payback time from 15 years to 25.
"The banks are rich, they've got money, they can afford to do it - and they will make their money in the long run."
'Enforce the right to housing now' is one of the main protest mantras
However, he also stressed that simply building houses was not the answer unless a sense of community could also be built.
"There is a very thin line between low-income and affordable housing," he said.
"We have seen slums move from one area to the next... drug pushing, prostitution, moves to the new area, and the new area becomes the slum."
But Joe Fontana, Canada's Minister of Labour and Housing, warned that while concerned parties have successfully raised awareness of urbanisation, "the fact is that those who are coming to our urban centres are deprived of basic human dignity."
"We've talked an awful lot of talk, but actually done very little," he added.
"It comes down to a question of political will... we have failed humankind by not making habitat the number one priority of governments around the world."