Rugged terrain, strong winds and darkness hampered the efforts of firefighters who battled the 13-hectare blaze on Browns Island this week.
Mysterious circumstances still surround the blaze, that has charred nearly half of the nature reserve and taken more than two days to extinguish. When authorities went to investigate smoke billowing from the island on Thursday, they found a woman who told them she had been stranded on the island since Monday and lit the fires to raise the alarm.
The woman was treated at Auckland Hospital for dehydration, but was resting at home on Friday. Police have not released any more details around how she got to the island, because she told her rescuers she did not know.
Browns Island, also called Motukorea, is a 5.5km kayak from St Heliers, and about 1.3km from Little Bucklands Beach.
Fire investigators said there was no evidence of a boat or kayak near the fire scarred areas, and they did not believe the woman would have been able to swim there.
Parnell Senior Station Officer Chonell Ford was in the first boat-load of crews to be taken to the island in the Hauraki Gulf by the police vessel, Deodar.
What was reported to be a small fire quickly ripped across the grass to cover nearly half the island, she said.
"As we started approaching the fire we saw the big plumes of smoke and realised that there was only a few of us over there and we didn't have enough manpower or equipment."
Ford said the woman was on the beach when they arrived.
She looked dishevelled, tired and upset, but did not say anything to Ford to reveal what was going on.
"We were mainly concentrating on extinguishing the fire," she said.
Crews used pumps to access the sea water, and later found a pond on the island to source water from.
The terrain and conditions were challenging, she said.
"There was a few hills and stuff around the place, but what made it difficult was that it was quite rocky. You would be walking over unsteady ground in the dark, and the hoses would get stuck in all the rocks."
Ford said she was on the island for about five and a half hours, leaving at about 12.40am on Friday morning.
Other crews worked through the night, from 11pm until 8am.
It was a very unique situation, she said.
"For a scrub fire it was pretty unique, definitely the terrain was challenging and the fact it was night-time, and the water source. The most unusual part of it was that there was a woman over there who didn't know how she got there."
Fire Service spokesman Shaun Pilgrim said the fire was "all but completely extinguished" this morning, with 20 personnel still out there.
Dangerous trees were being felled, and crews were expected to leave on Saturday afternoon.