A person, a lighter and sleeping supplies were all things found or seen in the vicinity of where the Government Garden blaze started, yet the cause is still unknown.
A sea of orange could be seen from the entrance of the Government Gardens as shrubbery in the area was engulfed in flames.
Seven fire appliances rushed to the scene of the fire about 4.30pm yesterday, where 40sq m of trees and shrubs were burning.
A witness said the flames were 10-feet high at one point.
Specialist fire investigator Lynda McHugh, who was sent to the scene, said the fire was easily one of the biggest she had ever seen in central Rotorua.
She said the fire had gone up "extremely fast" in "extremely dry" conditions.
McHugh was able to find the point of origin for the fire, but could not quite determine what had happened.
She said the fire being deliberately lit had not been ruled out.
A lighter was found on the scene, however it did not work.
In dry conditions, something as small as a cigarette can ignite flames, she said.
A person was also spotted in the exact vicinity moments before the fire started and this sighting has been reported to police for further investigation, she said.
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She said it was clear a number of people had been living in the area as there was a range of items including sleeping gear found.
Fireworks and sulphur had both been ruled out as causes, however, as the heat in the ground was so strong, McHugh said small sulphur fires had popped up 20 to 30m away.
Sulphur fires released dangerous toxins when burning, so firefighters approached the blaze with care.
Investigations into the cause would be ongoing, she said.
By about 5.30pm, firefighters were damping down hotspots and the fire was extinguished completely by 7pm.
Witness Koinonia Kiripatea-Smith, who called emergency services, told the Rotorua Daily Post yesterday that the heat from the flames was "strong and scary".
She was driving back from Sulphur Point with her mother when she thought she saw fog coming from the direction of the museum.
"We carried on to the Government Gardens and we started to see smoke. By the time we got there the flames were 10-feet high and it was hot and the smoke was thick.
"Within two to three minutes it had spread up a tree which is how it got so high."
Kiripatea-Smith said people were trying to move their cars out of nearby parking spots as the fire took hold.
"I was standing about 150 feet from the flames and it is hard to describe that heat. It was strong and scary."
Concern grows for Hayden Kemp, 40, last seen in Rerewhakaaitu on Friday.