Plans for a landmark underground cultural centre at Barangaroo have quietly been downgraded to a ''gloomy cavern with no sun'' and independent scrutiny of the project is inadequate, a former state government adviser says.

It has reignited debate over design standards at the prized harbour-front site, where the government is considering James Packer's proposal for a 60-storey hotel-casino.

Earlier designs for an underground cultural centre at Barangaroo.

The Planning Department has approved changes to a giant cultural ''bunker'' set into a headland being built at the north end of Barangaroo, including an apparent reduction in size and removal of key architectural elements.

A member of the former Barangaroo design excellence review panel, James Weirick, described the changes as ''pragmatic, cost-cutting solutions'' that failed to create a ''proper architectural entry of great moment'' for Sydney Harbour.