UPDATE: Specialist fire inspector Stuart Bootten said the investigation into the fire at Sulphur Bay that started on Sunday has come to an end.
"We have determined it as undetermined. We just can't pin point the cause, there's just too much destruction. We know where it started but don't knowhow it started," Mr Bootten said.
The information Mr Bootten and his team have gathered has been given to the police who he said would appreciate any further information that anyone might have.
EARLIER: Fire crews have kept a close watch overnight on the scene of a massive fire near central Rotorua while experts try to work out how the blaze started.
Rotorua Lakes Council principal rural fire officer Richard Horn said they were still to determine what caused the fire in Sulphur Bay yesterday afternoon.
"There are still a few active hot spots through the area including a few sulphur fires," Mr Horn said.
A firefighter was on standby at the scene throughout the night to make sure the fire was contained and to ensure there were no reignitions.
Image 1 of 13: Scrub fire in Rotorua. Photo/Ben Fraser