Stats NZ has finally begun to release information from the bungled 2018 count, when one in six New Zealanders didn't fill out a questionnaire as it went online for the first time.

The country's statisticians embarked on a "large scale mitigation process" to fill gaps, assuring Kiwis of the reliability of the count.

As of March 2018, New Zealand's population stood at 4,699,755, with the country projected to break through the five million mark in the second half of 2020.

Fuelled by migration, the country has grown 2.1 per cent from the 2013 count; the largest growth rate since the 1970s.

The proportion of Kiwis born overseas is now 27.4 per cent, up from 25.2 per cent in 2013.

"The growth in overseas-born population coincides with higher migration over the last five years, especially by young adults coming to study or work in New Zealand," census general manager Kath Connolly said.

New Zealand is experiencing a historically low unemployment rate of under four per cent, and an annual growth rate of 2.1 per cent - well above the OECD average.

The census shows the country's changing demographics.

For the first time in more than 40 years, the median age has dropped, from 38 years to 37.

The "European ethnic group" share, as classified by Stats NZ, dropped from 74 to 70.2 per cent between counts.

The biggest jump came from the "Asian ethnic group", up from 11.8 per cent to 15.1.

Maori and Pacific Islander populations are up, both in raw figures and as a percentage share, but that growth is in part due to a methodology change.

Stats NZ has used administrative data to ensure the historically under-counted population is represented on the stats sheet.

There are now 185,955 fluent te reo Maori speakers in New Zealand, up almost 50,000 from the last census.

Auckland, which topped a population of 1.5 million for the first time, remains the country's biggest and most multicultural city, with greater Maori, Pacific Islander and Asian population shares than across the rest of the country.

But it's the regions around Auckland that are the fastest growing.

Northland and the Bay of Plenty - the regions north and east of the major Kiwi metropolis respectively - were all up by three per cent annually.

Those boosts in population will result in the North Island awarded a new electorate for the 2020 election.

Christchurch is also back up and running.

After recording a decrease in population of 7,000 in the 2013 count, the South Island's biggest city has grown by more than 20,000 people to rebound from the devastating 2011 earthquakes.

The city's Selwyn district was the second-fastest growing municipality in the country, behind tourist town Queenstown.

The South Island's remote West Coast was the only region to head backwards since the last census in 2013, down 573 people or 1.8 per cent.

Australian Associated Press