Super city mayoral candidate Len Brown has blasted his rival John Banks' vision to bring the 2020 Olympics to Auckland as a "flight of fancy".

Mr Banks surprised the Government by last night announcing he wanted to bring the Olympic Games to Auckland in 10 years' time.

"This is the Auckland mayor who has refused to build a pool for the community in Otahuhu yet now he wants to spend billions - the budget for the Rio de Janiero games is around $17 billion - on an Olympic bid," said Mr Brown, the Manukau City Mayor.

"I think we need to get our transport system sorted out before we go off on flights of fancy about spending billions for the Olympics. Fixing transport is what I'm focused on."

Selection for the 2020 Games has not yet begun, but is expected to attract bids from the world's major cities, with a winner to be announced in 2013.

Mr Banks spoke last night on Radio Sport about how Auckland had won hosting rights to the 2012 Triathlon World Championships - and then suggested the city should follow it with a bid for the Olympics.

"Let me share with you a 2020 vision. I haven't told anyone else but I have a 2020 vision," he told the radio station.

Mr Banks went on to explain that Auckland's bid for the 2018 Commonwealth Games had fallen over due to a lack of investment, infrastructure and time, but the Olympic Games were "a different kettle of fish".

"Can you imagine in our lifetime bringing the Olympic Games to the southwest Pacific, Auckland? How good would that be," he said.

He had talked to his "friends" in Wellington who were also having a "light-handed look at the opportunity", he said.

But a spokesperson for Prime Minister John Key told TVNZ that the news was a surprise to him.

Mr Banks had raised the idea in passing with the Prime Minister some time ago, but at no stage had there been any meeting or proposal with either the Prime Minister or Minister for Sport and Recreation, the spokesperson said.

On Newstalk ZB this morning, Mr Banks said there had so far been nothing firm done about his idea except for a quick chat with Mr Key.

"There's been no proposals, no engagement with Wellington, but it's just one of those big vision ideas I have that one day, well into the future, when we can afford to do these things, we should have a look at it."

A spokesman told nzherald.co.nz today that Mr Banks would not be making further comments because at this stage it was just an idea he had thought would be worth exploring and having a conversation about.

North Shore Mayor Andrew Williams called Mr Banks's suggestion a "pie in the sky idea of grandeur".

Hosting the Olympics would cost billions and would be too expensive for a country with fewer than five million people, Mr Williams said.

Mr Banks should not be sidetracked from Auckland issues, he said.

The 2016 Olympics' four host city finalists, Rio de Janeiro, Chicago, Tokyo and Madrid, proposed budgets of up to $17 billion.

Their populations range from just more than 3 million in Madrid to up to 39 million in Tokyo's metropolitan area.

The eventual winner, Rio de Janeiro, put forward an overarching budget of $17 billion, which included $1.8 billion on security.

About a quarter of its smaller organising committee budget, of about $4 billion, is to be paid for by public funds, split three ways between the federal, state and city government.