Train service at five stations on the North East Line (NEL) was disrupted after a train broke down at Clarke Quay station towards Punggol.
Service between Outram Park and Farrer Park stations was affected for about 11/2 hours, during which a rescue train was used to push the defective train out.
"The push-out was completed at about 7.50pm and service progressively returned to normal," SBS Transit said in a statement.
"We apologise to affected commuters for the inconvenience caused. Meanwhile, we are investigating the cause of the fault," it said.
The operator had sent out a public alert at 6.20pm that journey time would be extended by 10 minutes, then it sent another tweet 12 minutes later that the additional time would be 15 minutes.
At 6.42pm, it announced that there would be free buses available at designated bus stops between Outram Park and Farrer Park stations. At 7.45pm, it indicated that the 12-car push-out had been completed, and that normal service was set to resume soon.
Such a push-out involves another six-car train being used to push the crippled train out of the way so that normal service can resume.
Retiree Kevin Tan, 57, was trying to take a train when he got stuck at Kovan. When he decided to give up waiting and left, he said he was charged 77 cents on the way out of the station, "but my wife who was with me wasn't charged".
"The station staff said I could come back within three days for a refund," he said.
The breakdown is the fourth in two days. On Wednesday, all three lines operated by SMRT experienced delays and disruptions.
Service on the East-West Line was tripped up by a two-train collision at Joo Koon station, and the Circle Line was affected by what was believed to be a door-related fault. Later in the afternoon, journey time along the North-South Line took 40 minutes longer than usual because several trains were pulled out of service.
These were trains of the same model as the ones involved in the Joo Koon collision, which was caused by a signalling fault.
SMRT would not say how many trains have been pulled out.