PERTH'S population is set to climb to three million and overtake Brisbane and Queensland's population will grow from 4.6 million to 7.3 million by 2075.
The latest population growth forecasts from the ABS also show the nation's population is on track to double in just more than 50 years.
Driven by births, life expectancy and migration, trends showed Australia's population could double any time between 2058 and 2101.
ABS demography director Bjorn Jarvis said by 2053, Melbourne and Sydney should be neck and neck for the most residents of a capital city, at 7.9 million people each.
"By 2040, Western Australia's population is projected to almost double in size, from 2.4 million people in 2012 to 4.7 million," he said.
"Queensland will have gone from 4.6 million people to 7.3 million, and the Australian Capital Territory will have grown from 375,000 people to 586,000."
In other areas the Northern Territory is on track to grow by 51% to 360,000 people by 2040, Victoria up 50% to 8.4 million, New South Wales up 35% to 9.9 million and South Australia up 26% to 2.1 million.
At the same time, the ageing population will push the number of people aged 65 or older to twice its current level, up from 3.2 million people last year to 6.8 million by 2040.
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