The substance behind more than a dozen hospitalisations after a reported gas leak in Auckland on Thursday is yet to be identified, with Fire and Emergency saying it wasn't a gas leak.
Emergency services were called to Augusta House on Victoria St West in the CBD twice on Thursday after people in the building became unwell. Fifteen were hospitalised and others treated at the scene.
Though initially reported as a gas leak, no trace of one was found.
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"I think we should stop calling it a gas leak, because I'm not sure that's exactly what's happened," Fire and Emergency assistant area commander Dave Woon told Newshub on Friday.
Firefighters have handed the scene over to WorkSafe, saying there's no risk of fire or explosion.
"We have tested for every hydrocarbon that we know of and there's no hydrocarbons there, so as far as flammability is concerned, I'm very, very confident that is not an issue," said Mr Woon.
"It's more of an odour... that's made people nauseous."
Evacuees couldn't agree on what the odour smelled like, however.
"When we arrived it was a pungent, caustic smell," said Mr Woon. "[I couldn't smell it] and most of our firefighters couldn't either... but it was also described to me as a chemical Janola smell, or a warm carpet smell - whatever that is. I said, 'You mean wet carpet?' and she said, 'No, warm carpet.' It's one of those subjective things."
While his view is there's "obviously something wrong", others are now wondering if it's a case of hysteria - more specifically, mass sociogenic illness.
"It's essentially when a group of people under stress experience physical symptoms that seem like they have a physical cause, but really it's a psychological cause," UCLA School of Medicine psychiatry professor Dr Gary Small told RadioLIVE.
"It spreads by social contagion among the group members. Often it is short-lived, but sometimes these outbreaks can go on for quite a bit of time."
He said people are often unwilling to consider the possibility of mass sociogenic illness because of the stigma.
"Often when investigators come in and they say, 'Well, this is something that's psychological,' the victims are often disturbed. They feel you're telling them it's not real. We're not saying that - the symptoms are very real, but it's clear that if there are certain patterns, it's likely to have a psychological cause."
Stress and anxiety are usually what sparks it, and it's spread by communication - in the past that would be newspapers and TV, nowadays social media.
"We found there was definitely a spread of symptoms according to the media coverage of these events," said Dr Small. "Today we don't need newspapers - we have the internet, which is spreading this stuff remarkably quickly."
There's even a possibility there was something in the air at Augusta House, but the response was largely hysterical.
"With all the toxic environmental risks and all the real threats out there, you can get a mixture of a real, physical cause of an outbreak and on top of that is anxiety, that causes psychological symptoms to spread."
Some famous examples of mass hysteria and sociogenic illness are detailed below.
The windshield pitting epidemic
In 1954, motorists in a small town in Washington began reporting holes and dings in their windshields. Soon people all over the northwestern US state were finding blemishes in their windshields - the blame fell on vandals, cosmic rays, nuclear fallout, fleas, radio transmitters and even Martians.
"It turns out those windshield pits had been there all the time - they just hadn't noticed it until they were anxious about the environment," said Dr Small.
At various times between the 14th and 17th centuries, groups of people in Europe would literally dance themselves to exhaustion - sometimes thousands at once. No cause has ever been pinpointed, with explanations including poisoning, epilepsy, spider bites, stress and curses. One suggestions is that people were actually performing ancient rituals banned by church, under the guise of dancing.
Fifty schoolchildren fainted at a Scottish primary school in 1981, and no cause was ever found. A similar incident occurred at a school in Blackburn, England, in 1965.
In 2011, 20 girls at a high school in New York started having involuntary spasms and twitches. The problem stuck around until the end of the school year in June 2012, and had significant media coverage. Doctors eventually concluded this was what kept it going - as the media coverage waned, so did the symptoms. By graduation, they all appeared to be cured.
In 2008, police in Congo arrested 13 'sorcerers' on suspicion they had been using black magic to shrink or steal men's penises. Alleged victims were trying to lynch the sorcerers.
"When you try to tell the victims that their penises are still there, they tell you that it's become tiny," police chief Jean-Dieudonne Oleko told Reuters.
He suspected it was a "huge joke", but others vowed it was true.
"It's real. Just yesterday here, there was a man who was a victim. We saw. What was left was tiny," one man told Reuters.