A computer generated image of what the five alternative flags could look like at Masterton's Genesis Recreation Centre.
Post offices taking ballots today before voting closes.
The design that will compete to be New Zealand's national flag is set to be revealed tonight.
Voting on the first flag referendum closes at 7pm this evening, and the Electoral Commission is expected to announce a winner out of the five alternative designs at 8.30pm.
The final result could still change depending on late and overseas ballots. An official announcement of the winning design will be made on Tuesday. That flag will then go head-to-head with the current national flag in a second referendum in March.
Ballot papers were still flooding in yesterday, and will continue to be accepted by the Electoral Commission up until 7pm tonight.
Those who had not yet posted their ballot papers can still deliver them by hand to a NZ Post shop today.
Prime Minister John Key, who launched the referendum process a year ago, said voter turnout was on course to overtake the last postal referendum in 2013, on the sale of state-owned assets.
"It shows you people are engaging," Mr Key said.
As of yesterday, 1,372,783 people had voted in the flag referendum. That amounted to 43.3 per cent of the voting population.
The turnout for the asset sales referendum was 1,368,925, or 45.1 per cent of the voting population at the time.
The most recent referendum on a constitutional issue, the MMP system, had a turnout of 74.2 per cent, though it was held at the same time as the 2011 general election.
Mr Key said he expected more people to take part in the second referendum because it decided whether the national flag was retained or not.
There is a possibility that some of the voting papers will be protest votes, and will not count towards the final result.
The Returned and Services Association has campaigned for people to spoil their ballot papers in protest.
New Zealand First leader Winston Peters said he had written "keep our flag" on his ballot paper, which meant it would be counted as an informal vote.
The process to pick a potential national flag has prompted heated debate across the country.
On Parliament's last sitting day, Leader of the Opposition Andrew Little said 60 per cent of Kiwis had "voted with their dustbin" on a change of flag.
The Labour leader urged the Prime Minister to "stop wasting money on his pet project and use it to help needy children instead".
The Government has said there is no chance the second referendum will be scrapped, no matter what the turnout is for the first referendum.
Silver Fern (Red, White and Blue) and Silver Fern (Red, White and Blue) by Kyle Lockwood
Kyle Lockwood could be the person behind New Zealand's new national flag, and he is a little nervous about it.
As the creator of two of the more popular alternatives, his name has been drawn into the heated national debate around changing the flag.
"It's pretty daunting, actually," he says. He admits he has been avoiding polls and commentary on the issue.
The Melbourne-based architectural technologist has also honed his arguments to defend his flag against staunch defenders of the status quo.
His designs are for people who want a change but do not want a clean break from the past, he says. "My flags are evolutionary, not revolutionary. This fern has been used by New Zealand for quite some time, since around 1888. It is part of our heritage as well."
He expects that once a single alternative design has been chosen by voters, more people might be converted to the idea of change.
"Once we've firmed up the idea, and there's only one flag, you might find that the polls could possibly change. It will come down to a knife edge. Anything could happen, really."
Koru by Andrew Fyfe
Andrew Fyfe says it is "quite surreal" to have his flag design scrutinised by the entire nation.
The Wellington-based graphic designer and photographer admits to being a "behind the scenes" person who avoids the spotlight. "I've tried to keep away from most flag-related things," he says.
When the referendum results are announced tonight, he will be squirrelled away in a bach in the Abel Tasman National Park, possibly without internet reception. "I may have to call a friend," he says. His family would be having a small flag-themed party, possibly with a koru-shaped cake.
The unfurling fern frond on his flag was "quite apt" for a relatively new, multicultural, environmentally minded country, he says. The current flag, on the other hand, has "never represented most of New Zealand".
A distant relative of women's suffrage leader Kate Sheppard, he likes change. "I don't like doing things just because that's the way they've always been done."
If Red Peak wins the first referendum vote tonight, it will mark an unlikely rise for a flag which was not even in the picture until a few months ago.
Its designer Aaron Dustin, 42, is the product design director for accounting firm Xero, based in Melbourne. Little is known about him. Unlike the other designers, he does not feature in the project's promotional material and he could not be reached for comment.
Mr Dustin submitted 18 designs to the flag competition. Red Peak was selected for the shortlist of 40 flags, but went no further. That prompted howls of protest from its supporters. After a massive groundswell of protest at its exclusion, the Government caved and added it to the final list.
Red Peak's official description is that it reflects "powerful and fundamental visual elements from New Zealand culture". The chevron is inspired by Maori weaving patterns and the two tectonic plates which form the Southern Alps. The red and black colours refer to the Maori creation myth Rangi and Papa. The red triangle with a white stripe hints at the stars from the existing flag.
Silver Fern (Black and White) by Alofi Kanter
Alofi Kanter says he is honoured just to have made it this far. He is a flight attendant and father of three with no experience in design, but has an interest in history and a keen eye for symbols.
Two of his koru designs made the 40-flag shortlist, and his preferred black-and-white design is now among the final five contenders for a new national flag.
"[The referendum's] not coming around every month or year or so," he said. "It's something we're not going to have again any time soon." He was born in Europe and raised in Samoa, where he was named Alofi. He felt black and white were New Zealand's de facto national colours, and should be recognised in its flag. Explaining his design, he said some white was added to give it balance and avoid comparisons to Isis' flag.
Mr Kanter will be in a Los Angeles hotel when the referendum results come in, and remains optimistic.
What happens next?
Today: 7pm: Voting closes on first flag referendum, which is between five alternative national flags.
8.30pm: Preliminary result announced for winning alternative flag.
Tuesday: Official result announced for first referendum.
March 3: Second referendum begins. Voters choose between winning alternative design and current national flag.