SAPS spokesperson Thulani Zwane told the BBC that the search for survivors would resume after some of the concrete blocks has been cleared.
Fifty are feared to be trapped under the rubble and one person has died while about 20 people have been rescued, according to reports, some with "traumatic injuries".
"It is going to be a long operation. It will take time to get to everyone," Netcare spokesman Chris Botha told broadcaster eNCA from the scene.
"It is extremely horrific... concrete big blocks have fallen on to people."
The accident happened around 16:30 local time on Tuesday.
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