Fire investigators say they are confident a campfire caused a 150-hectare scrub fire that cut off the town of Glenorchy and took out power to hundreds of homes.
The Otago Regional Fire Authority, aided by the police, began an investigation into the blaze this morning.
Deputy Rural Fire Officer Jamie Cowan said it had determined a campfire on the beach below Rat Point ignited the blaze, but it was not clear who the beach-goers were.
The area is a well known illegal camping spot.
"Those responsible may have already left the scene on Tuesday evening thinking that their campfire was out, before wind blew hot embers into the surrounding dry vegetation."
He said investigations were continuing and they were appealing for sightings of a white van in the area on Tuesday afternoon.
"If anyone has any information that could help us out, we ask that they please get in touch while it is still fresh in their minds," Mr Cowan said.
At its peak, eight helicopters and 50 ground crew were called to fight the fire. Firefighters went out again this morning to extinguish hotspots.
Otago is currently in a restricted fire season, which means any outdoor fire in the region needs a permit.