At least 50 people were injured when a railway maintenance locomotive rolled into a passenger train at Mamelodi, Pretoria.

An investigation is underway to determine what caused the locomotive, known as a tamping machine, to collide with the Metrorail train just after 6pm at Eerste Fabrieke Station on Saturday.

There were approximately 300 people on the Metrorail train.

“The tamping machine rolled from Greenview back to Eerste Fabrieke station where the Metrorail train was stationary and carrying commuters on board,” Metrorail Gauteng said in a statement.

Emergency services attended to 43 minor and 14 serious injuries. “The injured commuters are receiving urgent medical treatment at both Steve Biko and Tshwane district hospitals,” said Metrorail.

“The driver of the stationary train requested the 300 commuters on board to leave the train upon noticing the oncoming tamping machine. The commuters refused to leave the train and instead pulled the passenger emergency alarm levers, which stops the train from moving.”

Metrorail said that the train service between Pienaarspoort and Pretoria had been affected.

"The line has been closed to allow both Metrorail and Transnet technical teams to attend to the accident."