"We'll start our scene examination in conjunction with the fire service. That will kick off tomorrow morning,'' Ms Howard said.
When fire crews arrived this morning, the house "well involved'', central fire communications shift manager Jan Wills said.
Six trucks and crews were needed to battle the blaze.
A neighbour of the elderly couple told Radio New Zealand the speed of the flames was terrifying.
Vivienne Boyle, who lived across the road, heard someone calling for help and went outside to see a young woman calling that the house was on fire.
"We could see smoke coming out and the start of some flames.
"It was pretty scary you could see that pretty soon the (front) room was about to be totally on fire.''
Ms Boyle said she knew an elderly woman lived in the house.
A person attempted to get into the property but the front door was locked, she said.
She and other neighbours were able to get close to the house and attempted to put the blaze out with hoses.
"The smoke was heading to the next house as well, so they were doing their best to quell the flames on the house next door.''
The flames moved "extremely fast'', Ms Boyle said.