Melbourne currently has about 100,000 fewer residents than Sydney, but social researcher and demographer Mark McCrindle is confident Melbourne "will take the crown in a few years".

He claimed Melbourne's population is growing faster than Sydney's because the Victorian capital beats its New South Wales counterpart in two ways.

"Firstly, affordability — house prices, as steep as they are in Melbourne, are significantly below Sydney's," McCrindle told radio station 3AW.

McCrindle claimed people are leaving Sydney for Melbourne, while the southern capital is also gaining more residents from overseas migration than its northern neighbour.

But neither regions are the fastest growing in Australia right now.

That title goes to south-east Queensland.

Melbourne has been Australia's largest city before.

"As a result of the Gold Rush and until the 1890's, Melbourne was Australia's largest city," the report read.

"But back then, Melbourne was a side show to Victoria's growth, home to just one in four Victorians."