The country’s electoral commission said 56.61 percent of voters backed the existing flag, while 43.16 favored a change.
The results are preliminary but the size of the margin means they are unlikely to change when the final tally is released next Wednesday.
The outcome will likely be viewed as a defeat for Prime Minister John Key, the main advocate for change, who described the existing banner as a colonial relic from the days of British rule.
“New Zealand has voted to retain our current flag. I encourage all NZers to use it, embrace it and, more importantly, be proud of it,” he tweeted.
Deputy Prime Minister Bill English said some would be disappointed with the outcome but the government had staged a robust democratic process that had given people a choice.
The referendum was the culmination of an often-heated 18-month debate which touched on issues of national identity in the South Pacific nation of 4.5 million people.
On one side of the ballot was the existing flag, a dark blue ensign with the Union Jack in the top left corner and four red stars representing the Southern Cross constellation.
On the other was the proposed alternative — a silver fern on a black-and-blue background, which retains the four stars.
Created by designer Kyle Lockwood, it beat four other proposed flags in a preliminary referendum last December, AFP reported.
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