Census field workers from a remote holiday spot say this year's survey was so haphazard that they were eventually told to skip some houses.
The workers feared that the digital-first approach combined with poor organisation meant that the poorest households in regional areas had been left out of the census.
The release of the 2018 Census data has been delayed until next year because of lower-than-expected turnout. The response rate of 90 per cent was the lowest in five surveys.
Hilary Falconer, a field officer in Matarangi on the Coromandel Peninsula, said she had worked on two previous censuses and found this year's experience "frustrating and confusing".
It was the first time Statistics NZ used a digital-first method, which encouraged respondents to complete the census online.
Falconer said field officers were not given paper forms for those without internet access, and instead directed people to a helpline where they could ask to be sent hard copy forms.
"That's the problem - they haven't captured, say, rural Maori, people who don't have computers. I didn't have a paper form that I could just hand them.
"I had people who were ringing up for days, trying to get on the helpline, and it was always busy or they were told to ring another number."
Matarangi is mostly made up of holiday homes which were empty during the census. Falconer said many did not have letterboxes.
"We've got nowhere to leave this envelope. And there was a panicky response from headquarters – leave it under a rock on the doorstep, or ram them under doorways or under pot plants."
During extensive training, officers were told to leave no stone unturned and find every person possible to complete the census.
But they were later advised not to bother with some hard-to-reach properties at the end of long rural roads.
"At the end it got so chaotic it never got followed up.
"There was a complete sense of panic toward the end that it hadn't worked out like they'd hoped."
Census General Manager Kathy Connolly said Statistics NZ was in the process of assessing the collection phase. That would include feedback from field officers, she said.
She said field officers had to follow new processes at this year's census, and received instructions in advance.
She did not respond directly to questions about whether houses were deliberately missed. But she said paper forms were given to officers after census day to follow until with households that had not taken part.
"Field officers completed nearly one million visits over seven weeks of follow-up across the country."