However, details about the manpower involved in containing and extinguishing the fire at the BDO building on Como St have been released.
Fire Risk Management officer Michael Upton said more than 100 firefighters and 23 appliances were required to fight the blaze on the fifth floor of the building.
Mr Upton also released photos of the scorched interior - showing how flames razed the floor and left the offices looking like a bomb site.
He said the Fire Service was alerted to the fire at 8.49pm by an automatic fire alarm activation from the building.
It was brought under control shortly after 10.30pm.
"Firefighters were required to conduct a search of each floor of the building as it was occupied at the time of the fire," Mr Upton said.
"There were no injuries caused by the fire and the building occupants managed to escape safely.
"The building had a robust evacuation scheme in place, and upon activation of the fire alarm the occupants knew what to do, which was pleasing to see."
Mr Upton said that while a considerable amount of damage was caused to part of the building, the fire was contained to the fifth floor, however smoke had travelled throughout the building.
Mr Upton said the blaze showed the importance to business owners and property managers the need for having monitored fire alarm systems and sprinklers within commercial buildings.
"This allows for early detection of fire and calls the Fire Service instantly, minimising loss and down time."
Firefighters remained at the incident overnight to dampen down any hot spots.
"At this stage the cause of the fire remains undetermined and fire investigators are still at the incident investigating. The building remains closed today."
At the height of the blaze more than 20 trucks and 80 firefighters were battling the explosive fifth floor inferno which broke out just after 9pm.
Witnesses last night described seeing smoke pouring from the building before an explosion shattered windows on the fifth floor, showering a walkway beneath with broken glass.
Videographer Daniel Hines said he counted five aerial units with large ladders, which were being used to douse the building with water.
Another witness said the fire appeared to be confined to one floor - but had spread very quickly.
"It was at least a quarter of the floor up in smoke," the man, who only wanted to be known as Sam, said.
"There are fire trucks everywhere and I saw one with a crane going up. There's water everywhere and smoke everywhere. It's crazy."
A New Zealand Herald reporter said a "massive hole" had been blown out of the north-west corner of the building on the fifth floor.
It measures about two metres by two metres.
A walkway beneath the building had been showered with shattered glass.
The fire was extinguished by about 10pm and all occupants are believed to be accounted for.
Waitemata Fire service area commander Denis O'Donoghue said emergency services were alerted to the blaze just after 9pm.
"When police arrived they were confronted with a fire coming out of the fifth floor window.
"By the time they got established it was coming out of a number of places in the building and they put an appliance up to the window and they had an attack from fire fighters in the stairwell and attacked it from the inside as well."
Mr O'Donoghue said the fire had been easily extinguished and it was lucky it had not been further up the building where it may have been harder for fire services to access.
He said damage was mainly restricted to level five, with minimal damage on level six.
"There will be some smoke damage in the rest of the building as well."
Mr O'Donoghue said the cause of the fire was unknown.
- By Regan Schoultz, Vaimoana Tapaleao
