Australia will welcome its 25 millionth resident late on Tuesday night.

The Population Clock estimated by the Australian Bureau of Statistics assumes an overall population increase of one new resident every one minute and 23 seconds.

The ABS estimates that at 11pm on Tuesday, the milestone will be reached - although it will be impossible to know who citizen number 25 million will be.

The 25 millionth person could be a newborn baby or it could be a person moving to Australia. (AAP)

If growth remains at this rate, there should be 26 million in another three years from now, and 40 million by mid-century.

"Our births are pretty even, with a fertility rate of about 1.8, which is pretty high internationally," says Director of Demography at the ABS, Anthony Grubb.

"And we've been welcoming 200,000 to 250,000 new arrivals per year for a decade or so now."

Australia will welcome its 25 millionth resident late on Tuesday night. (AAP)

It's impossible to say exactly who this will be - it could be a newborn baby or it could be a person moving to Australia, but what we do know is that overseas migration is fuelling population growth (accounting for 62 per cent), and the vast majority of new arrivals will make a life in our cities.

The Population Clock estimated by the Australian Bureau of Statistics assumes one birth every one minute and 42 seconds, one death every 3 minutes and 16 seconds, one person arriving to live in Australia every minute and one second, and one resident leaving the country to live overseas every one minute and 51 seconds.

That's an overall population increase of one new resident every one minute and 23 seconds.

Our annual population growth sits at 1.6 per cent, slightly higher than a global growth of 1.2 per cent and the highest of the G12 nations.

The 25 millionth person could be a newborn baby or it could be a person moving to Australia. (AAP)

This means we'll probably stand at 26 million in another three years from now, and if growth remains at this rate, there should be 40 million of us by mid-century.

As a country, we're more diverse than ever.

Our newest Australians from overseas are most likely to be from China, which accounts for around 16 per cent of new arrivals, and now 2.2 per cent of our population. Our proportion of Indians and Filipinos is also on the up (the percentage of those born in the UK and New Zealand, by contrast, is decreasing).

Australia will welcome its 25 millionth resident late on Tuesday night. (Getty)

As a whole, two-thirds of us live in capital cities, "and we're expecting that to nudge a little bit higher as time goes on," Mr Grubb says.

There are serious concerns that our cities, already squeezed, will barely cope.

Sustainable Population Australia estimates the required extra infrastructure for each additional new resident could cost well over $100,000 each.

Paul Jones, Associate Professor of Urban Planning at the University of Sydney, says our capitals are already in "a catch-up position".

"At some point you just can't keep adding one car after the other and thinking it's all going to work out. We're adding people to systems and streets that were never designed to carry such capacity."

(AAP)

The rush to develop carries with it a range of negative consequences, such as sky-rocketing real-estate prices, long commutes to work, heavy traffic and infrastructure shortfalls, and more waste - and the lower your social demographic, the more severe the effects.

We're also mourning green space. Australia is losing two million hectares of land to urban sprawl each year, according to a Sydney University seminar earlier this year. Much of it was used previously for primary production or existed as a habitat for our native species.

"It's a question of balance," says Prof Jones.