"I am still traumatised by what I saw," the worker said.
A cafe worker from Columbus coffee said she was shaken by seeing the man's body slumped on the ground of the atrium, in view of lunchtime diners.
"None of us knew him, but it was horrendous. Thankfully the incident happened before school finished."
Another woman said: "Everyone is traumatised and lots of people are getting counselling".
Dr Sarah Hartnall from Shore Clinic was on her way back from lunch when she saw the man at the bottom of the stairwell.
"I called my colleagues Dr Peter Adlam and nurse Joel Razon - we all tried to resuscitate the man," she said.
"I was walking past and saw him and called for help. I started to resuscitate him but he wasn't responsive - there was nothing we could do".
A police spokesperson said the man could not be named until all of his next of kin have been advised.
The spokeswoman said "there do not appear to be any suspicious circumstances and the matter has been referred to the Coroner".
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (Mon-Fri 1pm to 10pm. Sat-Sun 3pm-10pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• Samaritans 0800 726 666
• If it is an emergency and you feel like you or someone else is at risk, call 111.