A state government decision to reject expert advice to buy land early and cheaply at Fishermans Bend could cost taxpayers hundreds of millions of dollars as planning authorities struggle to provide community facilities and infrastructure for the precinct.

And the government's promise to deliver affordable housing as part of the urban renewal project is under question after it quietly abandoned social housing plans and as property prices skyrocket.

Affordability specialist Dr Judith Stubbs, a former government housing adviser, has called for 20 per cent of new housing to be set aside to ensure lower-income Melburnians are able to live in the precinct.

"Otherwise, as research in Melbourne and Fishermans Bend indicates, there would be no housing available that would be affordable for very low and low-income groups to buy or rent," she said.