St John Ambulance northern operations manager Greg Scott said they had minor injuries.
"There were scrapes and bruises and bumps and minor abrasions. We took them [to hospital] for an assessment."
Details were sketchy but it looked as though the floor and stairwell gave way. He thought the workers fell a couple of metres.
"By the sounds of it they were lucky to walk away from it."
He said the area resembled "a bit of a war zone".
The site where the staircase collapsed was not accessible to the public.
Inspector Matt Sillars said the accident happened when the workers were demolishing the staircase and "something has given way. What caused this is up to the Department of Labour".