Police and Fire and Emergency NZ are investigating whether the fire that started on Nelson's Rabbit Island yesterday afternoon was deliberately lit.
In a statement Police say, "initial indications suggest the fire may be suspicious and Police are working together with fire investigators to determine the cause of the fire".
The Rabbit Island fire is separate to the 1900 hectare fire still burning in nearby Pigeon Valley that started on Tuesday.
Police would like to speak to anyone who was on the island yesterday from around 2pm onwards or has any information which may help with their investigation, acting Tasman District Commander Zane Hooper said.
Officers are maintaining a strong presence in the community day and night as they continue to patrol the affected areas, police said.
Police have asked members of the public to remain vigilant and to report any suspicious or concerning activity to police on 111.
Anyone with information on the fire can contact police and fire investigators on (03) 546 3895.