Fire and Emergency says the firefighting efforts on Matakana Island will continue until at least Wednesday.
The blaze, which broke out on Saturday night, has already burnt through more than 37 hectares of scrub and pine slash.
It was contained on Sunday night but 30 firefighters and three helicopters have continued to work through on Monday to keep it under control with fire breaks.
Incident Controller Jeff Maunder says in some areas the fire is burning underground in the roots of large trees.
"The fire is contained within a secure perimeter, but there are pockets of vegetation and tree stumps that are still smouldering and could reignite if not fully extinguished."
Maunder said drones would be deployed overnight using thermal imaging to identify hotspots so that those areas could be targeted on Tuesday.
Resident Hauata Palmer said the fire did not appear to pose a danger to residents.
The fire was closer to the side of the island facing the Pacific Ocean, whereas most residents live on the other side, Palmer said.
The community was currently not affected by the smoke, because the wind had been blowing the smoke away from the settlements, she said.
Residents in nearby Tauranga say they have been able to see the fire from the town, and some even felt the smoke drifting over.
"There has been smoke and stuff come over and I've had other people complaining about respiratory ailments that, you know, they couldn't hang the washing on the line or had to shut all the windows and turn the air con on," resident Leanne Swinburne said.
Fire crews have been very swift in tackling the blaze, Swinburne said.
Boats had been regularly stopping off at the island to drop off firefighters, she said.
"I think that everyone's done as much as they could with the resources they have. I mean there's only one fire truck, I believe, on the island itself ... they did everything as fast as they could, I don't think there's anything that could've been done any better or faster."