The population of Auckland is predicted to hit 1.5 million some time this week.
The country's biggest city is expected to reach the landmark about Wednesday, based on average population growth over the last two years, Statistics New Zealand's population statistics manager Andrea Blackburn says.
"The 1.5 millionth person could be a migrant coming from overseas or from within New Zealand, but it is most likely to be a new baby," she said.
That's because births add more than net migration.
Auckland hit the 500,000 mark at the 1961 Census and in 1996 topped one million.
New Zealand's population exceeded 1.5 million at the 1936 Census. At that time Auckland was home to 17 per cent of the country's population. That share doubled to 34 per cent by 2011.
Statistics NZ predicts Auckland will top two million around 2036.
Auckland's population is less than Sydney, Melbourne, Brisbane, and Perth, but more than Adelaide.
NZN