A woman found stranded on Browns Island while a major fire burned had lit fires to get attention, police say.

A fire burnt through 13 hectares of scrub on the uninhabited island in the Hauraki Gulf last night and this morning. Firefighters contained its spread this afternoon.

While monitoring the fire last night, a police helicopter found a woman on the island. She was picked up by the police vessel Deodar and taken to the mainland.

The woman was taken to Auckland Hospital, and treated for dehydration, but the police said she had no fire-related injuries.

She told them she became stranded on Monday afternoon but was able to access food and shelter in a hut on the island.

She lit and extinguished small fires to attract attention from passing boats, but last night's fire got out of control due to wind, they said.

Detective Sergeant Tony McKenzie said police were still trying to figure out how she came to be on the island.

The woman had been treated at hospital and was resting at home, Mr McKenzie said.

There were concerns for her mental wellbeing and they would like to hear from anyone who might have seen her on the island since Monday, he said.

Photo: RNZ / Dusko

About 30 firefighters from various Auckland stations had trouble containing the fire overnight, but principal rural fire officer Bryan Cartelle said two helicopters with monsoon buckets helped bring it under control this morning.

"We've knocked it down significantly - we've actually stood the helicopters down at the moment ... and we've got ground crews in there at the moment opening up some of the hot spots so we can start dampening down again."

Deputy principal fire officer Scott Marchant said firefighters struggled to tackle the fire overnight because gusty winds were fanning the flames.

This evening, Mr Cartelle said the fire was not expected to spread further.

"The crews have felled several trees on the island to minimise any further risks, and we expect the team to be returning to the mainland at high tide this evening."

A woman whose home looks out to the island, Vicki Thode, said she did not notice anyone on the island. She saw only saw smoke and flames.

"All night long it was blazing bright red. By the time it got to the top of the island, we were watching it, making sure the wind wasn't actually going to change direction and come straight back at our house, which would have actually smoked it out, but it didn't."

Browns Island, which is also known as Motukorea, is an unoccupied pest-free reserve frequented by shorebirds like the endangered New Zealand dotterel and the variable oystercatcher.

It is more than 5.5km out in the gulf from St Heliers in Auckland's Eastern Bays.

Photo: Supplied / Waitakere Volunteer Fire Brigade