<p>

Almost 10 million migrants over the next 50 years will swell Australia's population to more than 40 million by 2060 and more than 50 million by 2100, under dramatically higher new projections by the Bureau of Statistics.

The projections, the first for five years, envisage tens of millions more people crowding into Australia's capital cities over the next 50 years, overwhelmingly due to migration.

By 2060, the bureau estimates, Melbourne will have 8.5 million people, twice as many as now. Even by 2050, it would have 1.2 million more people than the state government assumed in its core planning strategy, Plan Melbourne, released last month.

By then Sydney would have 8.4 million, an increase of 80 per cent from now. Perth would more than double to 5.5 million people, and Brisbane to 4.8 million. Both cities would be bigger than Sydney is now. Melbourne would overtake Sydney in 2053.

Those four cities, the migrant magnets of Australia, would add 14 million of the 18.4 million extra people envisaged by 2060.

The rest of Queensland would add 2 million, the ACT would double to almost 750,000, but in much of the rest of Australia - South Australia, Tasmania, and regional NSW and Victoria - population growth will either reverse or slow to minimal levels by 2050.

The bureau puts forward three sets of projections based on different assumptions about birth rates, death rates, migration levels and interstate movements, which provide a range around its central projection.

The high projections envisage an Australia of 42 million people by 2050 and 70 million by 2100. Even the low projections would see the population grow from 23 million now to 34 million in 2050 and 42 million by 2100.

Its central projections, which are those used in this article, would see Australia grow to 37.5 million in 2050, and 53 million by 2100.

Migration would become the driving source of Australia's growth. The bureau's central projection assumes a long-run average net gain of 240,000 migrants a year, roughly current levels.

That already generates 60 per cent of Australia's population growth, but that would rise to two-thirds over the forecast period as the society ages.

The bureau produces new projections every five years after the census. After the population boom since 2006, it now envisages much faster growth ahead than it foresaw five years ago, especially in Melbourne and Perth.

Sydney, however, is tipped to hold on to its crown as Australia's biggest city for longer than some have speculated.

On these figures, Melbourne would only gradually draw level before overtaking Sydney in 40 years' time.

Long before then, Perth would have overtaken Brisbane to become Australia's third-biggest city by 2028, with the ACT overtaking Tasmania in 2038.

Clique