Christchurch has narrowly retained its spot over Greater Wellington as the country's second largest urban centre.
Provisional estimates from Statistics New Zealand show there are just 600 more residents in Christchurch. Last year the centres were just 100 people apart.
Natalie Jackson, from Waikato University's Population Studies Centre, says the figures cannot be read on their own.
She says they do not yet show breakdowns, such as by age group, which can affect a population's long-term sustainability.
Overall, the figures show 76 out of every 100 New Zealanders live in the North Island.
The provisional statistics, based on census information combined with births, deaths and migration data in the year to June, show Auckland's population as 1,272,800, Christchurch 390,300 and Wellington 389,700.