Australia's capital cities will more than double in size within 50 years under current immigration rates according to research findings conducted by the Department of Immigration and Citizenship.
The research has also found more than 430,000 hectares of land will have to be made available for housing in both Sydney and Melbourne if net overall immigration remains above 260,000 a year.
Interestingly, even with zero migration, the capitals will grow in size by roughly 50 per cent, costing residents an extra $1000 a year due to added congestion within the next two decades.
Lead researcher Dr Jonathan Sobels, from Flinders University, said farms and public land would be consumed as bulging cities expanded.
"Sydney and Melbourne will rise to something of the order of seven million people. We've got something in the order of half of that now," he said.
"Where are they all going to go? They're not going to all go into 50-storey apartment blocks.
"Physically, the demand on land is going to be immense."
Affluence is forecast to rise faster under higher immigration scenarios, driving up the use of space and resources.
Per capita wealth would rise by about 2.3 times by mid-century with migration at the level of 260,000 a year.
Without migration, per capita wealth would double over the same timeframe.