Rail passengers angry at service delays torched at least 26 train carriages near Johannesburg on Wednesday evening.
Carriages were burnt at three different locations south of the city, causing 200m rand ($30m) worth of damage.
The arson followed service delays reportedly caused by technical faults. A shortage of trains has now caused services on one route to be suspended.
It was the second time in a week that trains have been torched because of poor services.
On Tuesday, passengers burnt four coaches after service delays apparently caused by the theft of electric cables.
Trains are used by many poor working South Africans who cannot afford cars.
Thandi Mlangeni, spokewoman for rail company Metrorail, said a signal fault at Midway in southern Johannesburg had brought trains to a halt.
"Passengers started getting off the train and burning it," she said.
The disruption had a knock-on effect, leading to delays in the Kliptown and Nancefield regions of Soweto, where passengers also then began to torch trains.
Service suspended
Wednesday's arson left Metrorail with no trains to run from Midway, in southern Johannesburg, to the town of Vereeniging, Ms Mlangeni said.
Commuters have been asked to use alternative means of transport.
The Star newspaper reports that minibus taxi drivers were charging up to four times the regular fare to commuters stranded on Wednesday evening.
Metrorail trains provide an important link for commuters between central Johannesburg, Soweto, and other residential areas further south.
Each train typically carries about 1,000 passengers.
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