Sydney will have to meet the challenges of an ageing population and a ''baby boom'', according to the latest growth projections for the city's suburbs.
Figures released by the NSW Department of Planning and Infrastructure predict an extra 2 million people will call the state home by 2031, when its population is tipped to reach 9.2 million.
Sydney's growth is expected to accelerate at a faster pace than the state, with the overall metropolitan population projected to be 5.8 million in two decades - an increase on the 5.6 million used for the government's draft Metropolitan Strategy released in March.
Sydney's older population is also expected to grow faster than anywhere else in NSW, with the number of people aged over 65 projected to increase by 90 per cent between 2011 and 2031.
Professor Peter Phibbs, the chair of urban and regional planning and policy at the University of Sydney, said the draft strategy had not adequately addressed the challenge of an ageing population.
''We've developed a lot of Sydney on the basis that people are driving around and they're located in bigger houses and they're very mobile,'' he said.
''A lot of older people are going to be less able to use a motor car and are more interested in community and public transport forms.''
Camden and Campbelltown, areas with high fertility rates, were still projected to have elderly populations increase by 328 per cent and 223 per cent respectively.
''They're going to have a population cohort that they're not used to before,'' said Professor Phibbs, adding solutions could be as fundamental as changing the phasing on pedestrian lights.
But Sydney will still retain a ''relatively young age profile'', the department's report said, thanks to a 40 per cent growth in the number of children in aged under 15 during the same period.
The City of Sydney's population is expected to more than double to 290,550, including a 96 per cent increase in the number of children under 15, in addition to a 137 per cent increase in the number of seniors.
Growth in the number of children is projected to outstrip the increase in the ageing population in areas like Woollahra, Waverley and North Sydney.
''You could almost call them the new baby boom in these high-value middle class areas,'' said Professor Bill Randolph, director of the city futures research centre at the University of NSW, who also expressed concern about the ways the state was preparing for the projected demographic trends.
''My fear is we're planning to cope with the new population in a very unsophisticated way.''
Department acting Deputy Director-General, Andrew Jackson, said the figures showed the importance of the strategic focus underpinning the new planning system.
''We will need to ensure that we understand and plan for these changes in our population make-up - for instance by supporting housing choice so that both elderly and younger people are able to live close to friends and family,'' Mr Jackson said.
Urban Taskforce chief executive Chris Johnson said the projections showed Sydney would need 100,000 more homes than planned in the next two decades.
A spokesman for the department said the implications for the revised projections on the state's housing and jobs targets would be ''closely examined''.