The current PM’s choice would be the silver fern on a black field, which is the symbol used by the national sports teams, especially the All Blacks:
Mr Key, who on Monday called an election for 20 September, said the vote would be held within three years.
The current flag shows the Southern Cross constellation and includes the Union Jack – the UK’s national flag – in one corner.
Mr Key said the flag represented a period of history from which New Zealand had moved on.
“It’s my belief… that the design of the New Zealand flag symbolises a colonial and post-colonial era whose time has passed,” he said in a speech at Victoria University.
“I am proposing that we take one more step in the evolution of modern New Zealand by acknowledging our independence through a new flag.”
Mr Key said that he liked the silver fern — popularised by national teams including the All Blacks — as an option, saying efforts by New Zealand’s athletes gave “the silver fern on a black background a distinctive and uniquely New Zealand identity”.