Auckland Council has narrowed down the options for a future city stadium to two proposals - one on the waterfront, the other a revamped Eden Park.

It has given both bids six months to self-fund feasibility studies and show why their proposal should be chosen.

Four options were in the running and councillors agreed on Thursday to shortlist a 50,000-seat facility at Quay Park favoured by New Zealand Rugby, and Eden Park 2.1 which would include a retractable roof and increase seating to 60,000.

Councillor Shane Henderson chairs a working group set up after council received unsolicited bids.

"Over the last few months, our working group took on the goal of exploring matters relating to Auckland stadium venues, and specifically to create a structured process for the numerous unsolicited proposals the council was receiving to build a 'national stadium' in Auckland," he said.

"The council was clear that this was not a council-initiated or funded project."

Henderson said the working group recommended the two frontrunners.

"This week, we've passed a milestone and we're now going to move forward to a feasibility study to look more closely at the future of a city stadium for Auckland."

He said they sought expertise in stadium operations.

"The process so far balances the need to move swiftly so we can provide certainty for the participants in the process, while also ensuring any decisions are informed by strong expert input."