Labour leader Phil Goff rejected mayoral pleas to reduce the height of the Mt Eden Prison development towering over the Southern Motorway when he was Minister of Corrections in 2007.

The sight of an eight-storey jail block taking shape alongside the motorway on the approach to Spaghetti Junction has horrified residents, principals and community leaders.

It has been blasted by Auckland City Mayor John Banks as an "architectural monstrosity".

Last night, Mr Goff was sticking by his decision to proceed with the new-look prison, saying while it might not be particularly beautiful, it would look like a commercial building and not be an eyesore.

"Yes, it is clearly visible from the road, but everyone has always known there was a prison there. This building will look less like a prison," he said.

Mr Banks and his predecessor as mayor, Dick Hubbard, wrote to Mr Goff and an earlier Corrections Minister, Damien O'Connor, accepting the need for some expansion on the site.

"What we are asking is a scaled form of development that respects the built environment around the area, rather than creating these three high-rise buildings with such a visual impact on this gateway into Auckland," their letters both said.

Mr Banks' letter said: "What we strongly oppose is that prison buildings will be built to 30 metres, which is twice the height of any other development that is permitted in the area."

In a written response to Mr Banks in November 2007, Mr Goff said he was satisfied the resource consent process had been properly followed by the Department of Corrections.

Mr Goff's position in 2007, and repeated last night, was that the prison project had been approved by council-appointed commissioners.

They were satisfied the heights of the buildings and their impacts on views to Mt Eden and the surrounding area "would not have a significant adverse effect on the amenity of the surrounding environment".

The views of the independent commissioners - Ross Gee, Kathleen Ryan and Eden-Albert Community Board chairwoman Lindsay Rea - were supported by the urban design panel, which argued that taller buildings allowed for the protection of the existing historic prison buildings.

Mr Goff said the council had a right to appeal the decision, but had chosen not to.

But Auckland City's planning general manager, John Duthie, said the council was unable to appeal the decision because the commissioners were acting on behalf of the council.

He said Mr O'Connor applied for an "outline plan of works" that overrode the district plan for a prison development with buildings of up to 30m.

Staff wrote a report saying the buildings should be reduced to the 15m zoning height for the area, Mr Duthie said.

He said the commissioners approved the project because their powers under an outline plan were limited - a view supported by a legal opinion from Buddle Findlay.

The new-look prison, due for completion by April, will provide 554 beds and support facilities that will be shared by the Auckland Central Remand Prison.

Many of the cells will be above the level of the adjacent motorway, but Corrections said the windows will be frosted to prevent inmates from seeing through them.

Neighbouring Auckland Grammar and nearby St Peter's College are concerned about the development.