A witness has relived the moment he realised there was something wrong, when an alarm rang out and he saw people evacuating SkyCity's convention centre.
"I just heard an alarm go off across the road, then saw black smoke coming out the top of the construction site and all the workers evacuating," he told Newshub.
"People on the floor above us said it was hot against the windows, but I didn't feel anything."
Courteney Maxwell, who was also in the area, said the wind was blowing the smoke across the city.
"It started as light smoke, but it's gotten darker as the wind blew it, it just became darker and darker."
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She said people on Queen Street are gathering to watch the commotion.
"People are lining up and watching it and the pedestrian crossing will go green, but no one will cross, they just stand there watching it."
Another witness said at first she wasn't sure what the smoke was.
"I looked over and was like is that clouds or smoke. Then we realised it was dark and it was definitely smoke."
She said the smoke is getting worse and is covering half of the Sky Tower.
"It was pretty big when we first noticed it, but it's getting bigger and it's getting darker. It's heading up half the Sky Tower and the wind is picking up again which is making the smoke pick up."
Newshub's Shannon Redstall says the smoke is dark and thick, and can be smelt around the CBD. She is looking at the blaze from the 27th floor of the nearby Council building and says the fire does not look under control.
Another witness told Newshub that the flames are about a metre high while a worker in a nearby building said the air conditioning had been shut down as the fire continued to rage.
Firefighters are battling to put out the massive fire at the SkyCity convention centre in Auckland.
Mayor Phil Goff said earlier the flames are out of control.
"The flames don't look to be under control at all at the moment. There are huge plumes of black smoke."
He said firefighters have arrived, but the flames are still burning across the building.
"The fire is now burning from the west side of the building all the way across to the north side, maybe 80 to 100 metres wide. It's burning on the roof.
He said there is likely to be substantial damage because of the fire's size and how long it has been burning.