A giant blaze that destroyed part of a Wellington marae was accidental - and probably started by hot embers from a brazier.

The probable cause of the fire at Tapu Te Ranga Marae on June 9 was "hot embers from a brazier being blown by strong winds and igniting combustible material near a storeroom in the main house building".

"The brazier had been used in an open area at the marae the previous evening, but was extinguished around 8pm because of concerns about ember transfer," the Fire Service said today.

A group of 36 people staying at the marae - including Scouts on a camp - were forced to flee the blaze. One firefighter received burns to his hands and was taken to hospital.

A total of 70 firefighters were called to the fire at the sprawling live-in urban marae at Island Bay.

Fire and Emergency Wellington area manager Dave Key said Tapu Te Ranga Marae had an unmonitored fire alarm system but it failed to operate on the night of the fire.

"This was because the alarm system had been isolated following a false alarm earlier in the week, but had not been reset by a technician as required."

Key said the investigation findings showed the potential dangers of using outdoor fires close to homes and buildings.

"This fire is a real tragedy for the marae and the wider community who use the facility. But it does demonstrate just how dangerous hot embers from fires can be, even when it's damp and cold."