Concerns about the structural safety at the Charlotte Maxeke Hospital, where a section of the roof collapsed on Thursday afternoon, were previously highlighted by DA provincial legislature member Jack Bloom.
Emergency services were still busy, going through rubble to see if people were trapped.
Johannesburg EMS spokesperson Nana Radebe said that, so far, one person had been removed from the rubble.
Bloom had previously raised concerns about the hospital.
In October 2016, he sent out a press release about issues he had picked up.
He had said there were "two buckets to collect water that leaks from broken ceiling panels on the hospital street level".
There were leaks in various rooms at a ward in the paediatric clinic and a consultation room was used for storage "because of faeces that leaked into it from the ceiling last year".
"Last year, surgery had to be stopped in one of the theatres because of leaking water. Large ceiling panels are missing at Ward 348 Radiation Oncology, with a huge bucket placed underneath to collect water," it said.
"There are also leaks in other parts of the hospital and in the parking garages. Sewage is sometimes mixed in as well, causing a foul smell."
Bloom, at the time, said: "I am concerned that structural defects at the hospital are causing the leaks, which management has done little to fix, despite many staff complaints. In 2012, there was a report on structural defects at the Charlotte Maxeke Johannesburg Hospital that warned that the X-ray department should be evacuated as it could collapse."
R50 million worth of urgent repair was needed deal with structural defects on the building's 5th floor.
It was not immediately clear if the issues Bloom had highlighted had been addressed.
In a report in 2012, the non-governmental organisation Section 27 highlighted the urgent need for infrastructure repairs at Gauteng hospitals in general.
"In many hospitals the buildings and infrastructure have not been maintained," it said.
"Wards are in a poor condition and are sometimes dangerous (for example, medicine storage rooms without burglar bars; a temporary psychiatric ward in which male and female patients are separated only by cubicles).
"Passages are often potholed. Doctors' quarters are often decrepit and uncomfortable. Various hospitals in Johannesburg have lifts that are often non-functional."