The government's plan to use Crown land for building houses in Auckland could be much smaller than originally thought.

Labour's housing spokesperson Phil Twyford says he has several well-placed sources, who have told him only a quarter of the planned 500 hectares will actually be usable.

He says the rest of the building areas are totally unsuitable to be built on.

"Including a cemetery, including school playing fields, including this electric sub-station and another one that we believe are in the list that his officials were using."

Twyford states a sub-station exploded only a year ago, which shows how dangerous the plan could be.