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.