New Zealand will go to the polls on September 20.

Prime Minister John Key announced the election date during his post Cabinet press conference this afternoon.

He said G20 summit hosted by Australia on 15-16 November was a factor in deciding the date.

Australia has invited New Zealand to take part in that summit, and Mr Key said there was a risk holding the election too close to the G20 would meant post-election coalition talks were still underway and a Prime Minister had not been officially anointed.


An election campaign could also mean other country's leaders could not visit in the lead up to that summit.

He said Parliament would rise on 31 July.

Mr Key would not say whether a referendum on the NZ flag would go ahead this election.

He said he would say more about the issue in a speech he was due to give tomorrow.

He has advocated changing the flag and has been considering a referendum.

Mr Key also said he believed elections should be held earlier than November in future, because of coalition talks.

National would campaign on its track record in education, health, law and order as well as the economy.

Labour leader David Cunliffe said he and his party were ready to fight the election and already in campaign mode.

"Bring it on.

"We are ready, we are up for this. It's game on."

He was not concerned Labour voters would be put off by the colder weather in September compared to the usual November date.

Mr Cunliffe has previously been critical of hosting the Royal visit close to an election, saying it was convention for a 6-8 month gap. However, yesterday he said the five month gap was "fine. We welcome the Royal family."

He said the election would be about the economy, a more inclusive society and "building a new passion for being New Zealanders - proud of our environment, culture and heritage."

Asked what he would bring to the role of Prime Ministership he said: "energy, passion, hope for a better tomorrow for all our children, and a united team that is right behind this effort to give New Zealanders the opportunities they deserve."

In 2011, Mr Key announced the election date in early February - nine months before the November election.

It is up to the Prime Minister to decide on the date. The regulated period for election spending and advertising now kicks in either three months before the election, or after the Prime Minister's announcement if that is within three months of the election.

Traditionally Prime Ministers have left it late to call the election to take advantage of knowing when the regulated period will start.

However, Mr Key said he does not necessarily agree that delaying it until the last minute gives a big advantage and it is in the interests of the voters and economy to have some certainty early.

Mr Key is also expected to give clearer indications of whether National will assist potential coalition partners in electorate seats closer to the election.

He has already indicated it will do so for Peter Dunne in Ohariu and Act's David Seymour in Epsom, but has not yet said whether it will support Conservative Party leader Colin Craig in the same way.

National ministers Paula Bennett and Murray McCully have both said they are interested in the two seats Mr Craig is most likely to be successful in - the new Upper Harbour electorate and East Coast Bays.