The latest projections from the Australian Bureau of Statistics shows Australia's population will double in the next 60 years, driven by strong increases in Victoria and New South Wales.

The bureau is projecting the population will soar from just under 23 million people to 46 million by 2075.

Western Australia is expected to have the largest rise, while Tasmania is the only state that is expected to see a decline in population.

The bureau's director of demography Bjorn Jarvis says by 2028 Perth will overtake Brisbane as Australia's third-biggest city, with 3 million people.

"And then 10 years later, the Australian Capital Territory [will overtake] Tasmania," he said in a statement.

"Melbourne and Sydney should be neck and neck by 2053, with 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.

"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."

The Northern Territory's population will increase by 51 per cent to 360,000, while Victoria's population will grow by 50 per cent 8.4 million.

In New South Wales, the population will climb by 35 per cent to 9.9 million.

Tasmania's population is tipped to level out by 2040, and then begin falling.

Average age to rise above 40

Meanwhile, low fertility rates and longer life spans are expected to increase the proportion of older people in Australia's population.

"In 2012 Australia's median age was 37 years old, by 2040 it could be 40.5 years," Mr Jarvis said.

The ABS predicts the number of people aged over 65 will double to 6.8 million people by 2040.

The number of people aged over 65 will almost triple to 1.2 million.

"By then, people aged 85 years or over will make up 4 per cent of Australia's population, compared to only 2 per cent in 2012,"the ABS said.

But Mr Jarvis says Australia's ageing population is not as big an issue as it is for many European countries and Japan.

"One of the results of having a reasonably robust migration policy is that you tend to have people entering the population that are in their 20s and 30s, so that helps to compensate for the broader ageing of the population," he said.

"So compared to a lot of other countries, Australia's ageing population isn't as much of a cause for concern."

The ABS has not dismissed the possibility that the national population could hit 46 million much sooner than 2075.