Statistics New Zealand has moved most of the 2018 Census online, but the elderly and others without access to the internet aren't too happy.
There are about 68 questions in this year's census - topics covered include transport, health, work, education and relationships.
Statistics New Zealand said codes have been mailed to every home in the country, and about half a million people have already sent in their details.
But it appears not everyone has received it yet, with some people contacting RNZ saying they weren't even aware the census was happening.
"Census? First I've heard of it! My computer is ready and waiting but no info received yet," said Penny from Golden Bay.
"No forms in this retirement village in central Auckland. Mail is not quick and easy since three days per week deliveries," said Glenys Griffiths.
"I live in a block of four units. Three tenants received codes, but I missed out," said Samuel from Takapuna.
"Seems that the census is not going to work as well as it should. I have not received a census form and I have not seen a contact number to phone to recover a paper copy. I don't have a computer," another listener said.
Kerikeri retirement village manager Hillary Sumpter echoed concerns, saying Statistics New Zealand hadn't thought about the elderly.
"Statistics New Zealand just don't seem to have allowed for the fact that a lot of people aren't going to be able to access this online, they don't have access to a computer, they might be visually impaired and they're elderly who have hearing issues, so it doesn't seem to have been very well thought through at all," she said.
Ms Sumpter said about 100 people didn't have their access codes and everytime they call the help centre, they keep getting different answers.
But 2018 Census general manager Denise McGregor said they expect everyone will have a code by 6 March.
"If they haven't got a code by the 6th of March they can ring in and ask for paper and if they want to fill it after the 6th of March, that's fine as well," she said.
Ms McGregor told Morning Report they're doing what they could to assist people.
"Our field staff will be out helping people in and around census day, we have screen readers for the blind and have been working with organisations to help people."
She said some people have had codes mailed on 23 February and others were still being delivered.
She said Statistics New Zealand have received feedback on how easy it was to complete.