Prime Minister John Key says he is happy with the flag referendum turnout, and that his first choice is the design that currently has its nose in front.
Preliminary results show the black, white and blue fern design is just ahead of the red, white and blue fern design, though the final count will not be known until Tuesday.
Speaking to reporters outside Auckland airport this morning, John Key said he has no concerns that nearly 10 percent of voting papers were informal or invalid.
"Look, it's one of things, if we change our flag, most people will look back two minutes afterwards and wonder what all the fuss was about. It'll be flown, it'll be work and it'll be celebrated."
He said he was "delighted" by the frontrunner choice.
"It was my number one choice but I also think we have a real contest now. You've got a flag which in a lot of ways was quite similar to our current flag but embodies the silver fern, which I think for a lot of New Zealanders is they would say is far more our national symbol than the Union Jack."
He said he had no concerns about the high number of invalid or informal votes.
"Some people were always going to sent in a protest vote like that, that's the nature of the referendum we're having. But 90 percent of people also put in a positive vote."
However, New Zealand First leader Winston Peters said many people would be wondering how the winning design actually won, as the runner-up was actually chosen by more people as their top pick.
He said the preferential voting system used was confusing and the fact that so many votes were informal or invalid will have disappointed those campaigning for change.
Too close to call
Once a final and binding result is released early Tuesday evening, it will bring an end to a lengthy process to decide which flag should challenge the country's existing one.
There were 10,292 designs submitted. This number was then whittled down to a long list 40.
That in turn was then slashed to 4 options in September by the Flag Consideration Project, but Parliament then increased the available alternative designs to 5 by including the Red Peak design.
The Black, White and Blue Lockwood design secured 50.53 percent of final votes, but this was only slightly ahead of the second-placed Lockwood design, which got 49.47 percent.
Flag Consideration Panel chairman John Burrows said that was far too close to determine a winner at this stage.
"My own view would be that currently it's too close to call because on first preferences the Red, White and Blue (second placed) Fern was slightly ahead.
"There'll be more results coming in on Monday and Tuesday so there'll certainly be more votes to be counted and it could change.
"So until 5 o'clock on Tuesday we're not going to know for certain," he said.
Click here to see a breakdown of the voting in the first referendum.
Click here to see how preferential voting works.
The Red Peak design, which was only added to the final shortlist after intervention in Parliament, came third place.
The Black and White Silver Fern came fourth, and the Koru design last.
The other options in descending order of preference
There were 1,527,042 votes cast in the in the first referendum - a 48 percent voter turnout.
"The turnout is not disappointing, you would always like more of course but it's a postal vote in between general elections," Professor Burrows said.
"The last referendum was on asset sales and that was 45 percent and this is higher than that, so it's not disappointing but in a democratic society you would always hope for more."
About one in ten votes, or 9.7 percent, were declared informal.
An informal vote can be where a voter leaves their paper blank, or takes deliberate action go ruin it.
"It's always disappointing to see an informal vote but the total proportion is relatively small, and I don't think it's affected the outcome very much," Professor Burrows said.
The New Zealand Flag Association said people who spoiled their vote in the first referendum wasted an opportunity.
Association president John Moody said he was not surprised at the number.
But he said it was still disappointing because people could have expressed their opinion if they had properly completed the forms.
If the preliminary Black, White and Blue Silver Fern winner is confirmed on Tuesday, the flag will be put against the existing one in a referendum in March.
The next referendum putting this Tuesday's binding winner against the existing New Zealand flag will be held between 3-24 March next year.
The Electoral Commission said if people got their voting paper to a PostShop before it closed yesterday, their vote would still be counted.
The official result will be announced on Tuesday 15 December. The official result will include those votes date-stamped by NZ Post before voting closed on Friday 11 December and received by the Electoral Commission by noon on Tuesday 15 December.
Referendum 'a good thing'
The first and second-placed designs are both designed by Kyle Lockwood.
Mr Lockwood said his anticipation had been building for more than three months since the announcement of the flag shortlist.
He said the referendum had been a good thing for the country.
"It's been an interesting debate and it's got people thinking about national identity for the first time. We've had a big conversation about that, and it's been a good thing for the country. There are a lot of people out there thinking 'hey, maybe now we're in the 21st century, maybe we could move forward with an identity of our own'."
The fact that just under 10 percent voting papers were left blank or spoilt was a sign of democracy at work, said the RSA.
President B J Clark said it suggested most people still wanted to keep the current flag in the second referendum in March.
"We will certainly be going out and encouraging people to - if they wish to retain the current flag - to ensure they will vote. At no point are we going to try and change peoples' minds. The one thing is that we are encouraging people is to put your vote in."
Mr Clark said the spoiled votes showed people exercised their right to show they did not like any of the alternative designs.
Deputy Prime Minister Bill English said the preliminary results of the first referendum showed "strong public interest"
148,022 informal votes. In the 2013 citizens initiated referendum on selling state assets, there were 4,167.— Mégan (@meganjwhelan) December 11, 2015
I know we exist in a bit of a bubble here but wow that choice of flag really drives that home— Justin (@LowScoreAttack) December 11, 2015