New Zealanders have taken on board official encouragement to fill out their Census returns online today, with one million forms completed soon after 1pm.

Census staff say their online computer system - which can be found here - is handling the high traffic volume well and don't expect any major problems ahead of the peak period tonight between 7pm and 10pm as the country records its statistical snapshot of its people in 2013.

Last held in 2006 and conducted every five years since 1851, the Census has been delayed only three times - due to the Depression in 1931, World War II in 1941 and the deadly Christchurch earthquake in 2011.

This year's survey is estimated to cost $72 million, slightly less than the $90 million budget for the 2011 Census because much of the preparation is already done.


About 7000 temporary staff will spend around 550,000 hours handing out and collecting 6.4 million Census forms - 1.8 million dwelling forms and 4.6 million individual forms for a population estimated at 4.46 million plus visitors, who must also fill in the forms.

Census spokeswoman Vikki Carter says the day has gone like clockwork so far, going over the milestone one million mark just after 1pm.

Area managers are reporting positive feedback from members of the public as they deliver forms to cruise ships, hospitals and airports.

But with five million forms still to go, the online system could still get bogged down.

"We're expecting around two million to be done online. The system will be completely fine for up to 200,000 forms per hour and if it gets busier than that it will slow slightly, but still should be fine," Ms Carter said.

Filling in the form should take a single person around 5-10 minutes, she said.

For a family with children, the time will vary depending on the age of the children.

If it's done online, once the age is entered, questions that don't apply will be greyed out and can be "really super quick".

General Manager 2013 Census Carol Slappendel says the process is the largest one-off activity being held in New Zealand this year.

She reminded people that being in New Zealand on Census night means they are required by law to fill in a census form.

"There are no exceptions," she said.

"From the tip of the North Island, to Stewart Island and the Chatham Islands, people will be filling in their census forms online or on paper, in English or Maori. Even people working at Scott Base in Antarctica, considered New Zealand soil, are counted during the census.

"The census is all about numbers. How many of us are there? How many of different ages? How many in different types of jobs and so on."

Collection starts tomorrow, and will take at least a fortnight.