More than 70 firefighters fought to cool 120 tonnes of melted glass that they said was "like trying to stop a lava flow" when a furnace began leaking at a Penrose glass recycling plant yesterday.
Several streets were cordoned off to divert traffic around the scene as 16 fire engines and support staff including ambulance and police officers dealt with the incident from until 2.30pm.
Police took away a man who became "confrontational" at one cordon, demanding to be let into his workplace.
Central Auckland fire district area manager Roger Callister said firefighters had been called to the site of O-I NZ (formerly ACI Glass) off Great South Rd several times - the last time about three years ago.
But he did not criticise the company, saying that holes in the furnace were a factor it had to deal with when working with the hot temperatures needed to melt glass.
The furnace that melts the glass ranges in heat from about 1100C to 1590C.
Mr Callister said glass began slowly spewing from a hole and burning paper and anything else it came into contact with about 11.45am.
Factory workers tried to cool the glass with water but this cracked the hot furnace further and the flow became too great, he said.
A fire alarm was set off because of smoke, and employees called 111.
Firefighters had to contend with extremely hot conditions both inside and outside the building as they fought to cool the glass, Mr Callister said.
The only way they could stop the glass flow was to hose it with water to cool it, which set off steam and left them with zero visibility.
"It's very much like being in a sauna that is totally full of steam, and a lot hotter," Mr Callister said.
O-I NZ staff would need to manually chip away at the spilled glass when it hardened to remove it before they could repair or place the furnace.
Company spokesman Dieter Lehmann said the glass was intended for wine and spirits bottles for both the export and domestic markets.
He said if there was any impact for customers it would be "extremely limited".
The company, which makes glass from raw materials as well as recycled glass, was not certain last night how long the furnace would be out of action.