The SkyCity inferno has reached the maximum "sixth alarm" - with more than 20 fire engines at the scene of the blaze, believed to have been ignited by a worker's blowtorch.
The worker is believed to have gone on a smoko break while laying down waterproofing material on the roof of the Convention Centre - but he left the blowtorch unattended, sparking the massive inferno.
There are unconfirmed reports that sprinklers in the $700 million building, which is still under construction, had not yet been installed.
Construction workers fled for their lives as a massive fire broke out on the top of the building. Hundreds of people phoned 111 as flames could be seen leaping from the Albert St building top at about 1.15pm. Workers could be seen fleeing the fire.
More than 20 fire appliances are helping battle a massive blaze that has engulfed Sky City's International Convention Centre which is currently under construction.
Specialist vehicles are even being called in from around the region as the scale of the emergency unfolded this afternoon.
Hundreds of people phoned 111 as flames could be seen leaping from the building top at about 1.15pm.
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Workers have fled for their lives in the confusion. Some initially thought it was a drill.
The staffer at the scene said they suspected the fire had started on the roof of the top floor. There are reports a worker left a blowtorch operating while he went on a smoko break.
"Then people said run, run and we knew we needed to get out." He had not seen any smoke inside the building.
Mayor Phil Goff said the fire appears to be out of control - spreading "massively" in the 15 minutes he and council staff had been watching it.
"The line of flames is going from one side of the building on the West right through to the East."
People from all around the city have reported seeing the smoke, including residents in Bucklands Beach.
Access to Sky City carpark and the Sky Tower are closed, but the casino remains open.
People are being evacuated from Hobson St, downwind from the smoke.