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 know how 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.