The flag debate is heating up - with a post by the Prime Minister supporting change attracting more than a million views, at the same time as one of his MPs came out against the alternative designs.

John Key has posted a message to his Facebook page making the case for a change, which has been seen by more than 1 million people since it was put up yesterday, and shared three times more than a post on election night last year.

Meanwhile, National MP Simon O'Connor has come out in strong support of the current flag - posting a video in which he shakes his head and laughs at the 40 proposed alternatives.

In a video posted to Mr O'Connor's Facebook page, the MP for Tamaki sits at his desk and points to the alternative flag designs, shaking his head and saying "no" to each, at times laughing at the designs.

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Mr O'Connor, who is on the board of Monarchy New Zealand, then turns to the current flag behind him and says, "yeah".

The video has been well received, with one person commenting that it "might get you a summons to the PM's office".

Mr O'Connor laughed at that suggestion, and said there were a range of views within the National Party on changing the flag, although he was unsure how many MPs wanted to keep the current one.

He said he had kept an open mind on a change, but none of the proposed alternatives jumped out. The video was a way to express his view to his constituents.

Mr Key' opponents to the process have labelled the referendum process his vanity project.

A long-list of 40 alternative flag designs has been released by a panel, which selected them from more than 10,000 submissions.

The panel is tasked with whittling down the shortlist to four designs for the first referendum in November and December.

Once an alternative flag is chosen, it will then go up against the current flag in a second referendum in March.

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Mr Key originally supported the silver fern with a black background, but changed his mind when it was compared to the Islamic State's flag. He now supports a design featuring the silver fern and southern cross.

Labour leader Andrew Little has said he did not plan to vote in the referendum because he felt it was not the time for Government to be spending $26 million on a flag.