UPDATED 5.46pm: New Auckland Mayor Phil Goff wants to make an early start on a $1 billion stadium on railway land alongside Vector Arena.

But Labour says it'll take a rugby world cup size event to make the waterfront stadium a reality.

In an interview with NewstalkZB's Tony Veitch today, Goff said he does not want to spend an estimated $250 million on upgrading Eden Park over the next 15 years and believes the spiritual home of rugby and cricket could be sold for as much as $300m.

LISTEN ABOVE: Phil Goff reveals his plan to Veitch on Sport.

Goff, who has only been in the mayoral job for two weeks, stressed the council did not have up to $1b to invest in a new stadium right now but if the council did not start planning it would miss the boat.

The mayor said private investment would be required and he hoped the Government might also provide some funding towards the project.

Labour Sport and Recreation spokesman Trevor Mallard said it's a great idea to prepare for the future, but the government shouldn't foot the bill.

"At the moment it's a bit of a pipe dream - I think it's a good idea to set the land aside but I don't think people should get their hopes up for it being done over the next decade or so."

There was only one suitable site left in Auckland which could be home to a long-mooted CBD stadium, Goff said, and that was the railway land next to Vector Arena close to the city's main rail, bus and ferry and motorway links. Ngati Whatua, who own the land, wanted to do a deal, he said.

"What a great place for a stadium. When I look around the city that looks to me to be the best option," Goff told Veitch.

"It's not as if we are going to have a new stadium in the next five or 10 years but it means we still have that option of putting a stadium in the right place. We really need to preserve that option."

Goff's enthusiasm for putting a CBD stadium back on the table follows a debate in March about the options, which included keeping Eden Park or building a new stadium on the waterfront, Wynyard Quarter, Ports of Auckland land or the railway land alongside Vector Arena.

Mallard said that it was a mistake to build Eden Park in the first place because of its location outside the central city.

He said it wouldn't be right to ask taxpayers to pitch in for the new venue.

"It's a really good idea to set aside land and to designate a space - but I think it's going to take a really big event to get the impetus necessary to get it built."

Goff said he did not want to put the cost on Auckland ratepayers if he could find alternative private funding, including sponsorship and naming rights - although history says the public purse picks up most of the cost and carries the risk for stadiums.

Goff said he had spoken with Warriors owner Eric Watson at the NRL Nines in Auckland where the rich-lister expressed putting money into a new stadium "and I should have got an IOU at the time".

"The private sector, I think, will come to the party to some degree, but also there is the opportunity again where we are going to have a national event where the Government is prepared to stump up and provide money like they did with the last Rugby World Cup. Nobody believes that is the last Rugby World Cup we will have in New Zealand," Goff said.

Watson and former America's Cup boss Stephen Barclay also talked about private cash to build a stadium. Vodafone NZ Chief executive Russell Stanners has also said he would "seriously consider sponsoring a new Auckland downtown stadium if it went ahead".

Warriors boss Jim Doyle has previously said a 30,000 to 40,000-seat, multi-sport, multi-purpose stadium would be great for the CBD.

Ngati Whatua's commercial arm chief executive Rob Hutchison yesterday said the iwi was open to discussions but there were many complex hurdles to building a stadium on the railway land.

He cautioned it would be difficult constructing a 40m high stadium on land with an 18m building height limit, protected volcanic viewshafts to the Auckland Museum and Parnell and rail and port access considerations.

It was also a tight footprint for a stadium and could involve realigning The Strand or Quay St, Hutchison said.

Goff said Auckland could not afford a white elephant, saying the 50,000-seat Eden Park was limited to 21 night events and would need another $250m spent on it over the next 15 years.

It was not his preference to spend that money on a stadium that could not be used for multiple purposes, saying the better option was to build a new 35,000-seat covered stadium for rugby, league, football and concerts.

A new, international stadium was needed as Auckland's population grows from 1.5 million to 2.5 million over the next 30 years, Goff said.

Former Rugby World Cup Minister Trevor Mallard, who in 2006 offered to build a waterfront stadium for the 2011 cup, said the idea of having a long-term plan for an Auckland central stadium was a good one.

A new stadium would be needed over a 50-year timeframe, he said, but believed it would have to be triggered by a large event and could not think what that would be.

"The time for the Government paying for it has probably gone . . . something Auckland is going to have to get its head around," Mallard told the Herald on Sunday.

He said a layered stadium might be best for Auckland, with 25,000 seats at the bottom level and 15,000 at the next level that could be locked off to reduce running costs.

Eden Park Trust Board chairman Doug McKay said Goff had not talked with the trust about his thinking, but hoped he would explore all options, including evaluating "the most obvious existing option" at Eden Park.

"The council has some big costings coming with the city rail link, moving the port and now a new stadium," McKay said.

A spokesman for John Key said the Prime Minister is yet to have a discussion with Goff about the matter.

"While the Government is currently focused on addressing higher priority infrastructure initiatives in Auckland the Prime Minister is open to hearing any such proposals from Mr Goff," the spokesman said.

In March, Key said a waterfront stadium was a good idea, but not a priority and doubted it would get off the ground.

-With additional reporting from Newstalk ZB's Alicia Burrow