Five people have been arrested in connection with fires on train carriages in and around Johannesburg, the city's emergency services said on Thursday.
The five were Metrorail employees, spokesman Robert Mulaudzi said.
Police could not immediately confirm this.
Three train carriages were set on fire at the Orlando East railway station in Soweto on Thursday night, Mulaudzi said.
"They are well alight. We are busy fighting the fire," he said shortly after 10pm.
On Wednesday night three train carriages were set on fire at the New Canada railway station in Soweto, and another two in Braamfontein, allegedly by strikers. Nobody was injured.