A leading statistician has supported Auckland Council's view that 1 million more people may be living in the city in 30 years.
The forecast is the highest of three trends projected for the city in the 30-year growth plan being debated.
Some critics of the city's blueprint have claimed the council is planning for growth that may not come.
However former chief government statistician Len Cook has told a gathering in Auckland that while there are uncertainties, the forecast is a realistic long-term view.
He says one third of the growth will simply be the longer life expectancy of the over-65s.
Mayor Len Brown says the scale of growth should prompt the Government to begin a debate on a national population policy.
New census data on Auckland's population is due in December.