The final four designs for a new flag for New Zealand have been unveiled, after being whittled down from a long-list of 40 and more than 10,000 total submissions.

Three of the flags use the fern symbol of the country while the fourth uses a koru, a Maori symbol of an unfurling silver fern frond.

A binding postal referendum will be held between November and December to find the country's preferred option, which will then be pitted against the current flag next March.

If one of the four flags gets more votes than the existing flag, it will be adopted by next September.