It's been confirmed the Middlemore Hospital's Galbraith building is 'earthquake prone'.

The building currently houses a birthing unit and two maternity wards, along with other units.

An expert seismic assessment shows the Galbraith building's just 20 percent of the New Building Standard.

It'll take up to three years, and more than 74-million-dollars, to bring the 50-year-old building up to the minimum building standard.

The board's yet to decide what to do.