The Department of Conservation says a fire that was lit on an island near Auckland with a total fire ban could have had "devastating consequences".
It said remains of a campfire and signs of a tent pitched on Pokohinu Island, also known as Burgess Island, was reported to DOC earlier this week.
The department's Great Barrier Island operations manager, George Taylor, said people needed to follow the rules.
"Burgess Island is one of the Mokohinau Islands that are significant for seabird and skink populations," he said.
"Fire is a serious threat to these and other wildlife and plants, many of which on the island could have been wiped out if the fire got out of control."
Mr Taylor said fires and camping were not allowed on the island.
The fire risk was currently high and the campfire could have easily spread, he said.
The Mokohinau Islands lie 100km north-east of Auckland city and Pokohinu Island is the only one that can be freely visited.
Permits are required to land on the other islands.