Kilometres of rail track was stolen from a company that repairs Metrorail carriages in Ekurhuleni.
Metal thieves used blowtorches to cut the track leading to the depot in Nigel.
Officials have visited the Union Carriage and Wagon (UCW) depot on Monday to inspect the site of the stolen tracks.
Initially, the length of rail track stolen was believed to be 2km, but it seems to have been much more.
The theft meant that no trains could enter or exit the depot, with several carriages now stuck inside.
Five men have been arrested in connection with the theft after they were found to be in possession of gas bottles used for blow torches.
UCW had not responded to a request for comment at the time of publication.
Mahlangu said UCW was responsible for repairs and maintenance of Metrorail trains, a division of Passenger Rail Agency of South Africa (Prasa).
“Our operations are not affected,” Prasa spokeswoman Lillian Mofokeng said on Wednesday morning. The carriages that were at the depot were not in operation anyway.
Mahlangu said he was unsure how the thieves had managed such a brazen heist as the depot was operational.
He said it was believed the theft had taken place at night.
In a separate matter, Metrorail trains were delayed across the East Rand on Wednesday morning due to cable theft and defective crossing points. The theft affected the routes between Germiston, Daveyton, Springs and Isando, among others.