There will be an extra electorate seat in the North Island at the 2020 election and roughly one-third of electorate boundaries will change as a result of population growth in Census 2018.
The Representation Commission will decide by April where the new seat will be.
The new data released today by Stats NZ means the number of general electorates increases from 64 to 65, the number of North Island general electorates increases from 48 to 49 and the number of Māori electorates remains at seven.
Stats NZ has confirmed one in six New Zealanders didn't complete a questionnaire "largely due to operational failures that made it difficult for them to participate''.
To address high levels of non-response, Stats NZ for the first time used alternative government data to fill the gaps.
But while Stats NZ gave itself a high quality rating for ethnicity data collected, the Data Quality Panel has lowered it to moderate.
The panel endorsed Stats NZ's decision not to publish iwi data due to the insufficient quality and noted "in this regard Stats NZ have not met their Treaty obligations to Māori".
A lack of staff and paper forms in some communities resulted in just 68 percent of Māori completing the census, which was conducted online for the first time.
Stats NZ said it was able to plug most of the gaps for Māori and Pacific people using other data, except for information about iwi-affliation for Māori.
The external panel said the quality of the data measuring the Māori population and electoral population data was accurate, but it refused to endorse the 'high' quality rating Stats NZ gave itself for ethnicity data, rating it instead as 'moderate'.
This data is "critical" for planning, for development of policies, meeting Treaty of Waitangi obligations, and addressing social inequities.
The panel found there was too much variability between ethnic groups, and inconsistency with the sources that information to fill gaps was gathered from, which means that any data comparisons with information prior to the 2018 Census should be undertaken with "extreme caution".
"There is now a break in the time series, that makes it very difficult to reliably compare 2018 Census results for ethnicity with earlier census, so this will affect the ability to monitor the change over time particularly for Māori and Pacific groups," Tahu Kukutai, one of the review panel members, said.
Concerns were raised by Te Mana Raraunga, a data soverignity group, last year about whether the low turnout rate for Māori would see the loss of a Māori electorate.
However, the number of Māori electorates has stayed at seven, with a net increase of 1200 registered on the Māori role, but the Māori descent electoral population has jumped by 18.7 percent, to 896,567.
Ms Kukutai said that is more likely a result of an undercounting of Māori for the 2013 census, rather than more Māori registering to vote.
Overall, the Māori population remains the second largest ethnic group, at 775,836 people, with a population increase from 14.9 per cent to 16.5 per cent.
The average age for Māori is 25.4 years, compared to 31.3 years for Asian, and 41.4 years for European.
The number of people speaking te reo Māori has risen from 3 per cent to 4 per cent of the total population.
Five million milestone in 2020
Statistics Minister James Shaw has welcomed the first release of 2018 Census data.
"I'm highly confident that the 2018 Census data will support the key uses of census information," Mr Shaw said.
"At recent population growth rates, we can expect to reach five million people some time next year, up from four million in 2003."
The results from today's data show New Zealand is becoming more culturally diverse while also growing.
"The census showed that 27.4 percent of people counted were not born in New Zealand, up from 25.2 percent in 2013. Those with an overseas birthplace were born in almost every country in the world, including 15 people born at sea,'' census general manager Kathy Connolly said.
The increase in the overseas-born population coincides with higher migration over the last five years.
The way the population is tracking New Zealand will hit 5 million people in the second half of next year.
The population hit just shy of 4.7 million at Census 2018 and on average the population grew by about 2.1 percent a year since 2013 - much higher than the annual average growth from 2006 to 2013.