The Wellington City Council is urging people not to light bonfires in the Botanic Garden.
The Fire Service said it was called to an incident in the gardens about 2am and found a group of people drinking around a small fire.
The police were asked to attend but no one was available, it said.
The council said it would make enquiries and assess if any damage had been done.
It said bonfires being lit in the gardens was a recurring problem.