Auckland's $3.4 billion City Rail Link from Britomart to Mt Eden has been delayed after an unnamed bidder withdrew from the process.

Chris Meale, CRL chief executive, issued a statement yesterday saying the release of tender documents for the tunnels and stations would be delayed by up to three months after a preferred bidder withdrew.

The eight bidders who pre-qualified were Acciona Infrastructure New Zealand, Bam International Australia, China Machinery Engineering Corporation joint venture, CPB Contractors, Ferrovial Agroman (New Zealand), Salini Impregilo S.p.A, Fletcher Construction and Vinci Construction Grands Projets S.A.S (VCGP) joint venture.

Meale said while the withdrawal of one was disappointing, it would not prevent progress on the CRL tender and discussions have already started with another prospective bidder, he said.

"We are fortunate that the initial line-up of eight bidders for the project was exceptional and it was a hard choice to determine the top two."

One made a commercial decision to withdraw this week.

"While we are naturally disappointed, we are moving on."

It is too early to tell if the three-month delay will roll on into the current project completion date of early 2024, he said.

Development opportunities for up to 20ha of new Auckland CBD and fringe city floor space were this week identified around the project.

Images were released showing development potential of the land once the project is done.