Queenstown and Auckland are studying the implications of latest projections which point to a population explosion over the next 20 years.
Statistics New Zealand figures show the Auckland region population will experience 60 percent of the nation's growth, taking its population from 1.37 million to 1.94 million over that time.
This means that the City of Sails will be home to 38 percent of New Zealanders.
The Queenstown region population is predicted to grow by 2.2 percent a year -- the highest growth rate in the country.
If the forecasts prove accurate, Queenstown's population will increase from 24,100 to 41,700 by 2031, with the number of people over the age of 65 tripling.
Auckland Regional Council's planning committee chairman Paul Walbren said planning was under way but there was still a risk the city's infrastructure would not be ready to match the population growth, especially in terms of transport. Queenstown Lakes District Council said it had done an independent analysis of the resort's population growth, which took into account visitor numbers.
Current numbers would double by 2026, said Queenstown Mayor Clive Geddes.
"Queenstown's average day population of around 35,000, will double to around 70,000, and our peak population, which is district-wide, will rise from 70,000 to around 140,000 by 2026," he told the Southland Times. Mr Geddes said preparation for growth was something the council had been prepared for, for a long time.
Of New Zealand's 73 territorial authority areas, 44 are projected to have more people in 2031 than in 2006.
However, population growth will generally slow over the projection period because of the narrowing gap between births and deaths.
