The government-appointed panel overseeing the project released its longlist of designs, chosen from more than 10,000 public submissions. 

The 40 will now be subject to further scrutiny, including an intensive intellectual property review, before being whittled down to four to be put to a public vote later this year.

A second referendum is planned for next year when the country will choose between the existing flag -- which features Britain's Union Jack -- and the most popular new design.

Project head John Burrows said the potential new flag had to be unmistakably from New Zealand and "celebrate us as a progressive, inclusive nation that is connected to its environment, and has a sense of its past and vision for its future".

"It is important that those designs are timeless, can work in a variety of contexts, are simple, uncluttered, balanced and have good contrast."

Common themes among the 40 flag offerings are silver ferns, the symbol used by New Zealand sports teams, and the Southern Cross constellation. Colour schemes are predominantly red, black or blue, and white. 

Prime Minister John Key, who has pushed for a change, favours a silver fern design to replace the existing flag, which has the Union Jack in the top left corner and four red stars representing the Southern Cross constellation on a dark blue background.

Many New Zealanders who took to social media to comment on the flag designs questioned whether the issue was important enough to justify the NZ$26 million (US$17 million) price tag.

The longlist of flags can be viewed at www.govt.nz/assets/Documents/Flags/The-long-list.pdf.