Doctors say fixing rot in a building at Middlemore Hospital in Auckland while patients inside have the potential to put lives at risk.

Counties Manukau District Health Board says it would not close the mould-infested Scott building while contractors replace cladding and frames.

Resident Doctors Association secretary Deborah Powell says dust and noise in a hospital is not ideal and neither is staff operating in unfamiliar settings.

"For instance, coronary care unit is set up to be a coronary care unit, so if we have to shift patients out of a coronary care unit we are putting them into a place that isn't built for purpose."

Ms Powell says it makes more sense to have a new building.