Visitors taking in Sydney's highest view from the Centrepoint Tower's Skywalk have been left traumatised after witnessing the moments leading to a woman's death.
It is understood she was with the group on the platform when she became "agitated" before taking off her safety harness.
Police were called to the scene with reports someone was threatening self-harm, but they couldn't get there in time.
The middle-aged woman dropped from the 268-metre tower to her death just before 3pm on Thursday.
For hundreds of tower tourists, an alarm sparked an emergency evacuation.
One woman was so severely traumatised, she was taken out in a wheelchair.
Skywalk is an open-air, glass-floored platform encircling the Sydney Tower.
Guests clip themselves into a safety harness and attach themselves to the building. Police will now investigate how that harness was able to be removed.
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The nightmare was also witnessed by those in nearby buildings.
Merlin Entertainments, the company behind the Skywalk, released a statement on Thursday confirming the incident.
"We are working closely with the police on this matter and it is being investigated accordingly," Divisional Director Rob Smith said.
"At this stage the Sydney Tower Eye Observation Deck and Skywalk are closed."
Initial reports had indicated the victim was a man, but police later confirmed her gender.
She has not yet been formally identified, police said.
Inspector Robert Winkler told reporters any witnesses in need of assistance are urged to contact their local GP or hospital to seek support.
"Support has been given to a number of witnesses, as well as police and emergency services," he added.
Anyone who witnessed the incident is encouraged to call Crime Stoppers 1800 333 000 or use the Crime Stoppers online reporting page.
For support and information about suicide prevention, call Lifeline on 13 11 14 or Suicide Call Back Service on 1300 659 467.