Staff in the City's SA Water building have been evacuated.
Early reports suggest a suspicious parcel was left at the delivery drop off area just after 10am.
Police have cordoned off the area and the bomb squad is on the scene.
The building is occupied by SA Water offices and the South Australian Tourism Commission.
Angas Street is closed between Victoria Square and Moore St, while evacuated employees are waiting at their emergency zones.
An update for staff is expected at 1pm.
More to come.