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KEY POINTS

* 100 firefighters still unable to bring inferno under control, despite dumping 12 million litres of water on blaze
* Several CBD buildings closed and staff sked to work from home
* SkyCity fire: Toxic smoke poses health risk for people in CBD
* Using monsoon buckets 'too dangerous' for fire crews inside building
* Fire traffic chaos: Roads jammed, workers told to stay home

The SkyCity Convention Centre has now been burning for more than 24 hours, with firefighters still battling for control and pumping 200 litres of water per second on the flames.

Fletcher Building has confirmed there were no active alarm systems on incomplete levels of the SkyCity Convention Centre- and the fire that turned into an inferno was first spotted by a supervisor.

The massive blaze has continued to burn since it started about 1.15pm yesterday - despite firefighters using 12 million litres of water as of this morning fighting the fire.

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Massive flames and black smoke continue to pour from the site with more than 100 ground-based firefighters using high-powered hoses to try to quell flames.

Fletcher Building CEO Ross Taylor told reporters today that the fire started where blowtorches were being used on bitumen to seal roof joints. The company remained committed to completing the $700m convention centre.

SkyCity boss Graeme Stephens said the fire was "absolutely devastating".

Fletcher Building later clarified that there were active alarm systems on all completed floors of the centre.

"It was on the floors still under construction where there were only manual alarm systems," a spokeswoman said.

The fire - ignited by a worker's blowtorch on the roof of the seven-storey building about 1.15pm yesterday - shows little sign of abating this morning. Flames and thick smoke continue to pour from the building.

"It's now got to the point where the regional commander has told me that they've abandoned the roof, they think that the roof might collapse so what they might try to do is stop the fire reaching below level five," Mayor Phil Goff told RNZ last night.

More than 80 firefighters are at the scene, with fire engines lined up Nelson St, as Auckland commuters face a morning of chaos and confusion. Many central city roads are closed, bus services are disrupted - and some businesses are urging workers to stay away today.

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The new SkyCity Convention Centre was still under construction. Photo / Dean Purcell
The new SkyCity Convention Centre was still under construction. Photo / Dean Purcell
The fire from above yesterday. Photo / Dean Purcell
The fire from above yesterday. Photo / Dean Purcell

Firefighters face a battle on another front this morning, with a severe weather warning forecast for Auckland - including heavy showers, thunder, hail and gales gusting 100km/h set to strike.

Meanwhile, a spokesman for Fire and Emergency New Zealand told the Herald there had been little change overnight.

There were 21 crews on the scene who were still in a "defence mode", he said, and the were continuing to let the fire burn through the roof.

In a slight reprieve for motorists, two lanes had reopened on Nelson St but Hobson St and Wellesley St West were also closed.

The Auckland skyline last night with smoke from the SkyCity International Convention Centre fire sweeping across the city. Photo / @yohophoto
The Auckland skyline last night with smoke from the SkyCity International Convention Centre fire sweeping across the city. Photo / @yohophoto

"Motorists are being asked to pass the scene slowly and with caution," the spokesman said.

He warned the public about the toxic smoke in the area and advised them to keep their doors and windows closed with the aircon switched off.

Fire crews last night sacrificed the roof of the Convention Centre to try to save the $700 million building.

Thick toxic smoke is still billowing across the CBD.

The inferno - believed to have been started by a worker's blowtorch - burnt overnight.

Fire and Emergency Auckland Regional Manager Ron Devlin said the SkyCity fire was one of the "largest and most difficult structure fires in recent times".

"It is a complex fire. In the roof ... bitumen, straw and plywood is compact and so we are having real difficulty getting into it.

Fire crews direct people through the area yesterday. Photo / Dean Purcell
Fire crews direct people through the area yesterday. Photo / Dean Purcell

"The roof is not safe to go onto, and the floors below are quite a distance below, so actually fighting and putting out the roof fire is very difficult.

"The plan was to cool and protect the area from surrounding parts of the building, but let the roof itself burn.

"It is the only safe way. It will take a while, 12 hours, maybe more.

"The fire is under control now, we are in a managed situation, we are just sacrificing the roof."

People cover their mouths from toxic smoke from the Skycity Convention Centre. Photo / Dean Purcell
People cover their mouths from toxic smoke from the Skycity Convention Centre. Photo / Dean Purcell

Firefighters have been diverted from as far afield as Hamilton to battle the blaze, believed to have been started by a worker's blowtorch on the roof of the new building. Sources say the fire ignited after the worker went on a smoko break about 1.15pm.

WATCH HOW THE FIRE UNFOLDED

Fire and Emergency assistant area commander Dave Woon said St John transported one person in a serious condition to Auckland Hospital.

The fire was "very difficult to extinguish" and was not yet under control. It started on the seventh floor and had since spread to the sixth floor. The fire has spread visibly across the rooftop in five hours, raising fears about the amount of damage.

The Auckland CBD was effectively sealed off for a large period yesterday with the closure of motorway on- and off-ramps. Officials warned people to stay away from the scene, amid fears of the toxicity of the smoke.

Auckland CBD was effectively sealed off for a long period yesterday with the closure of motorway on- and off-ramps

"It is a large fire, involving gas cylinders ... bitumen layers ... it is a very, very difficult fire to extinguish," he said.

"We are not on top of the fire, but with the resources just arrived we should be able to make progress."

Fire trucks had arrived from Hamilton. Woon said they had enough fire resources currently, but not if there was another major event.

Woon said the cause of the fire was not of concern at this stage.

But it is believed to have been started by a worker who went on a smoko break and left a blowtorch unattended.

Downtown Auckland is filled with billowing black smoke - which police warn could be toxic.

SkyCity casino and the Sky Tower have been evacuated and are closed until further notice. SkyCity hopes to be able to reopen its hotels and restaurants by lunchtime on Wednesday.

Parts of Nelson Street and Wellesley Street are closed while firefighters battle the blaze, and traffic around SkyCity was gridlocked for large parts of Tuesday. NZ Transport Agency is urging motorists to avoid the area.

Auckland office block air-conditioning units are being shut down to stop them dragging fumes and smokes into nearby commercial towers.

Account manager Charli Farman was sitting at her desk when she noticed smoke and told a colleague "I think it's on fire".

"It was a really small amount of thick black smoke."

"Then all of a sudden it was flames and really dark smoke."

Farman said a man in an orange construction vest was standing at the top of the building when the fire started.

"He was standing at the back for about four minutes but then he just ran when the flames started to spread".

Construction worker Sandeep Patel said he was inside the building that is now on fire and had been evacuated.

"We have no idea what is going on, all of a sudden we were told to get out."

Auckland Mayor Phil Goff is reporting what he can see live on his official Twitter page.

"Fire is really building. People can be seen on the roof,'' he wrote.

The SkyCity Convention Centre
• The $700m project is well under way, and is due to hold its first conference in October next year.
• Site: 1.4ha
• Floor space: 32,500sq m
• Equivalent to 4 rugby fields
• 33 meeting spaces of various sizes
• 5 times larger than existing NZ convention space
• Able to host events for up to 4000-plus people
• NZ's largest theatre, able to seat 2850 people
• NZICC designed by Warren and Mahoney, Woods Bagot, Moller Architects
• 303-room 12-level Horizon Hotel by Warren and Mahoney, Moller Architects