An "extraordinary surge" in population has pushed Victoria to the top of the national ladder after it gained an extra 97,500 citizens in the year to   March, a growth rate of 1.7 per cent. 
The next fastest-growing states, NSW and Western Australia, had growth rates of only 1.4 per cent, which was also the national average and the slowest rate for a decade.
Australia's population growth rate is now well below the 2.1 per cent achieved during the height of the mining boom and below the 1.5 per cent per year assumed in the intergenerational report.
The slowdown is the result of both a slide in the birthrate and a sharp fall in so-called net overseas migration as fewer immigrants come to Australia and more Australians move overseas.
Victoria has also benefited for a surge in internal migration, as relatively affordable housing and good job prospects make it a magnet for the rest of Australia.
In the past six months, 37,800 Australians have moved to Victoria from other states and only 31,900 Victorians have left.
By contrast 45,400 Australians moved to NSW but 48,800 NSW residents left.
Victoria and Queensland are the only two states gaining population as a result of interstate migration.
Demographer Bob Birrell from the Australian Population Research Institute said conditions in Sydney were driving the exodus to Melbourne.
"If you want a freestanding house in Sydney for less than $600,000 you have to move out 55 kilometres," he said. "In Melbourne you can still get one for $300,000.
"I am actually a little surprised that more Sydneysiders aren't moving to Melbourne."
Immigration was also feeding the extraordinary surge in Victoria's population. Although NSW received slightly more immigrants than Victoria, Victoria received more as a proportion of its population.
Population projections produced by the Bureau of Statistics have Melbourne's population exceeding Sydney's on two of the three scenarios modelled.
Under the "high fertility, overseas migration and life expectancy" scenario, Melbourne's population would be 9.193 million by the middle of the century and Sydney's 8.431 million.
Under the "medium fertility, overseas migration and life expectancy" scenario, Melbourne's population would be 8.162 million, and Sydney's 8.124 million.
Under the "low fertility, overseas migration and life expectancy" scenario, Melbourne's population would be 7.353 million and Sydney's 7.716 million.
Dr Birrell said the projections assumed that recent rates of population growth would continue, something that was unlikely. The Melbourne CBD simply couldn't keep growing as fast as it had because it would run out of room.
The bureau had assumed that the mining boom-related surge in immigration would continue 40 years into the future.
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