Crews were alerted to the leak in Pharmacy House on the corner of National Circuit and Brisbane Ave via a triple zero call just after 1pm and evacuated the building as a precaution.

The leak is in the Plant Room which has affected the three storey building on the lower levels.

It is currently being isolated by ACT Fire & Rescue, but some damage has been sustained to the ceiling and lights.

Some workers will soon be permitted to return, but only to the ground floor at this stage.

The two fire pumpers and one Commander are expected to depart shortly.