By Russell Palmer, of RNZ
Special votes can be returned and counted up to 10 days after election day so there is something of a lag time.
There are an estimated 480,000 votes (17 per cent of the total) still to be counted, and they could make slight changes to the election result.
Here's what they are, why they're special, and what you need to know about them.
What special votes are
Special votes are those that are not on the printed electoral roll, or are not taken at a voting place. The voter must also sign a declaration form.
They can include post-in and overseas votes, and votes made by people who have enrolled after writ day, which this year was September 13. It also includes prisoners who are on remand and - for the first time in a decade - prisoners who have been sentenced to less than three years.
They also include votes by people who have cast their vote from an electorate they are not enrolled in.
Special votes also include votes where people have cast an electorate vote for an electorate they are not enrolled in. These are still counted as party-only votes.
People who may not have been able to get to a voting place can include people who have chosen to vote by mail for various reasons including illness keeping them at home or in hospital, or people who can satisfy the returning officer that going to a polling place would cause hardship or serious inconvenience.
People with a physical disability which means they cannot mark their voting paper can also vote using a phone dictation service.
Presumably this year that will include some people who are in managed isolation.
Some people may also not wish to be listed on the roll, and so choose to be entered on the unpublished roll.
This year for the first time, people were able to enrol to vote at a voting place on election day. These votes - having been enrolled after writ day - will also be counted as special votes.
How are special votes counted?
Special votes can be returned up to 10 days after election day.
They must be counted in the electorate they were cast for, so it can take some time for the voting paper to reach the right place.
The vote must be checked against the electoral roll, and if the voter is not on it, the vote must be confirmed and the voter is added to a list of voters not on the roll before being added to the official count.
What effect do special votes have?
Last election there were 446,287 special votes - 61,524 of them from overseas - accounting for 17 per cent of the total of 2,591,896.
This year's numbers are similar, with an estimated 480,000 votes (again, 17 per cent of the total) still to be counted.
Special votes are typically more left-leaning votes.
In 2017, after special votes were counted, National lost two seats, Labour lost one, and the Green Party picked up two. In 2014, National lost two seats, with Greens and Labour picking up one each.
The same kind of slight changes could happen again this year, but they are unlikely to fundamentally alter the balance of power in Parliament.