He said the cause of the blaze remains unknown.
A St John spokesman said four people were treated at the scene and none required transporting to hospital. He said an earlier report that three were transported to Dunedin Hospital was incorrect.
Two firefighters on a ladder truck were earlier seen battling the blaze, which now appeared to be contained.
A St John ambulance arrived at the scene after 12.30pm and people were seen leaving the building coughing from smoke inhalation.
An uninjured man had been rescued from the roof and brought down in a cherry picker.
The man, who lives in a flat in the building, said he was told by firefighters to make his way to the roof where he was lowered to safety uninjured.
The Otago Daily Times has been told the fire began in a couch, but the source of ignition was not known.
Police officers from Dunedin Criminal Investigation Branch were at the scene.
An officer at the scene said it was too early to determine the cause of the blaze, but there was nothing at this stage to suggest it was deliberately lit.
Crowds of office workers massed at the police cordon as the firefighters attempted to douse the flames.
Witness Angus McBryde said people were seen leaving the building on the corner of Moray Place and Princes St while coughing.
Smoke was visible coming from an office building close to Rialto on Moray Place just after midday.
A witness said there were two fire appliances at the scene as of 12.05pm and there had been evacuations from the office building and neighbouring buildings.