CANBERRA, Feb. 23 (Xinhua) -- Australia's peak infrastructure body has called on the federal government to ensure that the nation's cities remain among the best in the world.

A landmark report released by Infrastructure Australia on Friday warned that the country's major capital cities are facing a decline in the quality of life and economic productivity if governments fail to plan for a population boom over the next 30 years.

Rather than recommending that population growth be inhibited, the "Future Cities: Planning for our growing population" report said that governments must plan for another 12 million people in major cities within the next 30 years.

Modelling found that Melbourne and Sydney were on track to grow to the current size of New York, London or Hong Kong by 2046, whose growth would cripple the cities without a national reform agenda to address infrastructure needs.

In addition to Australia's two biggest cities experiencing growing pains, the report also warned that Perth and Brisbane would be the size of current-day Sydney by 2046.

"Australia's cities are the powerhouses of our economy and they need to be a national priority of government," Philip Davies, CEO of Infrastructure Australia, said in a statement.

"Asia's global middle class as well as our own rapidly growing population will unlock new economic frontiers for Australia, but we need to position our cities to take advantage of this historic opportunity.

"Australia needs to start setting national objectives that allow our cities to realise their full potential and remain globally competitive."

Under the Economic Intelligence Unit's Global Liveability Ranking, Australia has three of the world's 10 most liveable cities, including Melbourne which is ranked No. 1.

However, Infrastructure Australia said Australian cities would slide down those rankings as traffic and housing affordability got worse with the population boom.

The report found that Sydneysiders were spending an average of 200,000 hours stuck in traffic jams in the morning peak hour every day. By 2046, it predicted that would grow to 400,000 hours.

Melbourne is confronted by similar problems with an additional 2.8 million people expected to call the city home by 2046.

"If Melbourne goes down the low-density path of unplanned -development on the fringe of the city, and there is no further investment in social infrastructure, our research found that people will be able to access up to 140,000 fewer jobs in one hour of travel," the report said.

The report modelled what all of Australia's major cities would look like in 2046 if they took on a high-density, medium-density or low-density approach to combating population growth.

However, Infrastructure Minister Paul Fletcher said that the models "may not be to everyone's taste."

"I am not going to predict which if any of these scenarios is likely to materialise - indeed I think the only thing we can confidently predict is that, like all predictions of the future, they are certain to be wrong in a whole number of ways," Fletcher said while launching the report.

Infrastructure Australia also found that small local councils were threatening urban liveability, urging the federal government to reward states with money if they can successfully simplify planning processes.

"The large number of small local councils in many of our major cities has resulted in cases of fragmented governance, and disjointed infrastructure and service delivery," the report said.