Firefighters are racing to contain a fire in St Paul's Anglican Cathedral in Dunedin's Octagon.
The fire broke out in the rear of the stately church building about 3.30am.
Seven fire crews have been called to the central city blaze, and a turntable ladder was being used to access the fire and bring it under control.
A Fire and Emergency spokesman said there were no indications the fire was suspicious, and there have been no reports of any injuries.
Fire safety investigators would be arriving at first light to determine the cause of the blaze.