Crews were notified following an Automatic Fire Alarm at the ACT Health Building on Moore Street, City at 7.03am.
Crews are conducting ventilation and air monitoring operations in the six storey building and have isolated the power to the ground floor escalator.
Three fire pumpers, the Hazardous Materials Unit, the Breathing Apparatus Van, the Bronto Skylift Hydraulic Platform and two fire Commanders are on scene.
Approximately 25 staff remain evacuated from the building.
Update to follow.