An earth tremor measuring four on the magnitude scale has been recorded in Johannesburg, the Council for Geoscience said.
Manager of the seismology unit Michelle Grobbelaar described the tremor as "quite a big guy".
The preliminary analysis indicated the epicentre was near the University of Johannesburg just before 10am.
One Twitter user said: "There was a tremor in JHB about 20mins ago. Building shook for about a minute. I'm still shaking".
Another tweeted: "Oh, so the tremor thing happened all over Joburg? Lol I thought it was just because of the construction in our office park".
Quakes, or tremors, are the result of a stress build-up in the earth's crust. When the stress becomes too great, it is released in the form of a quake, usually on a geological fault line.
Grobbelaar said previously that after an earthquake, it was a rule of thumb that another tremor of similar magnitude could often be expected in the same region, but seismologists could not predict when this would happen.
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