Fifty-six per cent of voters wanted to keep the existing flag, while 43 per cent wanted to adopt the silver fern design.

More than two million people have now voted in the flag referendum, as the finishing line approaches.

New Zealanders will learn tonight whether a proposal to ditch Britain's Union Jack from the national flag has been successful, with opinion polls indicating they will stick with the existing banner. "I encourage all NZers to use it, embrace it and, more importantly, be proud of it".

Prime Minister John Key, who was the main advocate for a change, accepted the people's decision in a tweet. Proponents such as Mr. Key cited Canada's 1965 switch from the Red Ensign to the Maple Leaf as a model to follow.

Seven Sharp reporter Kristin Hall, tongue firmly in cheek, posted a picture of a new design for the "next" referendum, showcasing "Flaggy McFlagface".

Another popular image is the Silver Fern, perhaps most commonly associated with the All Blacks, New Zealand's all-conquering rugby team. Voters chose the fourth option - in blue/black - in a 2015 referendum but have now voted to keep their current flag.

"I don't think we should shy away from having a discussion about contentious issues just because they are, by nature, contentious", he said.

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But large portions of the address boiled down to a general election response to hard-line rhetoric coming from Cruz and Trump. All three remaining Republican candidates have been invited to attend the black-tie dinner, according to the state party.

Last year, more than 10,000 public flag design submissions were whittled down to a long-list of 40 by the 12-member flag consideration panel.

The referendum was the culmination of an 18-month process that is estimated to have cost over $17 million - a price tag that is also believed to have put off some voters.

Andrew Little, leader of the center-left Labour Party, said New Zealanders had rejected the new flag as Key's "personal crusade" which had divided the nation.

Key had promoted the referendum and Lockwood's design, saying it would be a flag New Zealanders would be proud to fly at home and overseas.

A definitive result, taking into account late postal ballots, will be announced Wednesday, the country's Electoral Commission said.

The Returned Services Association, which had campaigned to keep the current flag, said it was pleased with the outcome of the referendum.