SYDNEY, Australia — The judges weighed 10,292 options — including a flightless kiwi bird firing lasers from its eyes — and the country spent two years thinking about it. But in the end, New Zealanders chose decisively to keep their century-old flag, a blue ensign with Britain’s Union Jack in the upper left corner and the four stars of the Southern Cross in red on the right.

Preliminary results of a nationwide mail-in vote, which pitted the incumbent against a flag known as the Silver Fern (Black, White and Blue) — showed on Thursday that 56.6 percent had voted to keep the existing flag flying, despite the assertion by Prime Minister John Key that it symbolized a colonial era whose time had passed.

“Naturally, I’m a little bit disappointed,” Mr. Key said at a news conference after the result was announced. “I always knew it was going to be a very tough thing to get more than 50 percent of people to vote for change. But the result was much, much closer than people predicted.” A recent poll had found that two-thirds of New Zealanders wanted to keep the existing flag.

Thousands of submitted designs — including the laser-equipped kiwi bird and a woolly sheep with stars for eyes, among less unconventional entries — were reduced to five finalists last year by a panel of 12 judges. Four of the five featured variations on a fern, a plant of symbolic importance in the native Maori culture (and the logo of the national rugby team).