New Zealand residents have voted to stick with their existing flag after a competition that attracted over 10,000 designs and a national referendum, estimated to have cost NZ$26m.

The preliminary results of the national referendum over the flag design were announced today, with 56.6 per cent of voters choosing to stick with the existing flag, which features a British Union Jack in one corner.

The alternative option, designed by Kyle Lockwood and featuring a silver fern, was selected after a multi-stage competition but only received 43.2 per cent of the vote.

The full results are expected to be confirmed on Wednesday.

New Zealand prime minister John Key had led the campaign to change the flag. Flown since 1902, the current design has a blue background, with the UK's Union Jack in one quadrant and a quartet of stars.

The government chose to crowdsource options for a new flag and invited members of the public to submit designs last year, with a long list of 40 announced in August.

A panel of judges then selected four of these for the public to vote on. The shortlist was unveiled in September, with three designs featuring a silver fern – a national symbol taken from a species of plant common in the country – and one showing a traditional spiral koru emblem, which is based on the image of an unfurling fern.

Another flag named Red Peak, designed by Aaron Dustin, was later added to the shortlist following a petition.

Melbourne-based Lockwood's Silver Fern design – with a leafy frond on a split background of blue and black – was announced as the winner in December.

This was then pitched against the existing flag in a postal referendum, in which more than 2 million people voted.

The process is thought to have cost more than NZ$26m (£12 million).

New Zealand is not the only country that has attempted to use crowdsourced designs. Last year, Qatar invited members of the public to suggest ideas for a logo and identity for its new National Museum.

Brands and designers have also been inviting the public to shape their work. Karim Rashid recently asked his Facebook followers to choose the facade for his building in New York and Porsche previously unveiled a unique version of its 911 car, which was voted for using social media.