Emergency services were called to the blaze on George St at about 6.20am on Thursday.
Fire and Emergency NZ spokesman said, on arrival, crews found one of several flats "well-involved" in fire and another flat smoke-logged.
"One person was unaccounted for at the time and crews commenced searching properties. We have since established all persons are accounted for.
He said damage to the front flat was severe and the smoke damage to the neighbouring flat was moderate.
The fire was extinguished by 7.40am and crews were still on the scene dampening down hotspots.
The cause is yet to be confirmed but it is not being treated as suspicious.