Firefighters could be seen entering the smoke-logged Severn St Kiwibank branch this morning.
A Fire and Emergency New Zealand spokesman said crews responded to reports of a roof fire shortly after 10am.
FENZ responded with two units, one from Oamaru and one from Weston.
A light fitting had caught on fire and dropped down onto the desk, causing the desk and items on top of it to catch fire.
The fire was put out shortly after 10.30am, the spokesman said.
The street outside the bank was cordoned off as firefighters worked and a fan was being used to ventilate the building.
A reporter at the scene said no fire was visible but there was a lot of smoke.