Australia needs to decide which towns will become big cities in the next 50 years as the population grows, the national infrastructure boss says.

As politicians debate migration, international students and temporary workers, Infrastructure Australia chief executive Philip Davies says a "national settlement plan" is needed.

"We need to get on the front foot in terms of pitching our horizon to the longer term," Mr Davies told AAP on Tuesday.

"What kind of cities do we want to have in 30-to-50 years' time?

"Where do we want to see the growth in some of our smaller regional cities and towns?"

Mr Davies, who will finish his term as Infrastructure Australia boss in August, said Adelaide, Canberra, Geelong and Perth had clear opportunities to take more people as the nation grew.

"At the moment the major heavy lifting is being done by Melbourne and Sydney. They're turning into truly global cities," he said.

"Some other cities like Perth are not seeing the same level of growth."

One measure could be for each state to identify a city or town it wanted to grow, and then partner with the national government to build industry and transport links over future decades.

"I often think about Japan and how their cities have grown along major high-speed rail corridors," Mr Davies said.

"That provides the reliable connections. Then you see the growth along those corridors."

He said high-speed rail between Melbourne and Geelong, which is being developed, could see Geelong become significantly larger.

But Mr Davies said the community needed to have discussions about what kind of cities it expects, and the lifestyles people want.

Liberal senator Dean Smith this week called for a review into Australia's population policy as the nation approaches 25 million residents.

Prime Minister Malcolm Turnbull said Australia's immigration and population growth was constantly under review.

He also said the federal government was building new projects, like the Western Sydney Airport, to meet rising demand.

"We are getting actively involved, we're building infrastructure ourselves," he told 3AW radio in Melbourne.