The tremor felt by residents of Johannesburg just before 07:00 on Friday morning was a "seismic disturbance" that took place near the Harmony Doornkop mining area, west of Johannesburg.

This according to Dr David Khoza, executive manager for applied geoscience and head of the seismology department at the Council for Geoscience in Pretoria. 

"The South African National Seismograph Network automatic locator detected a seismic disturbance near Harmony Doornkop mining area on Friday, 1 March, 2019 at 06:56 South African Standard Time.

"The event had a primary magnitude of M=3.8.

"This is an automatic location and magnitude which may change once reviewed by a seismologist.

"This area falls more or less in the West and Far West Rand mining region. Moderate seismicity had occurred before in the Far West Rand gold mining areas with four events of magnitude M=3.8 and higher from 2005 to date," Khoza told News24. 

It was a very light tremor, as those with a magnitude of M=2.5 or less are usually not felt, but can be recorded by seismograph.

Residents in the Johannesburg area took to social media on Friday morning in reaction to the tremor. While some were concerned, most reacted with typical South African humour, with one person apologising, saying he wouldn't have beans for breakfast again.

People reported windows and buildings shaking and the word "tremor" was trending within minutes.