Commuters saw their journeys disrupted by separate faults on the North-South and North East MRT lines yesterday.
On the North-South Line (NSL), a maintenance locomotive that stalled at Raffles Place station shut down northbound train services between Marina South Pier and Newton from the start of service till about 6.50am.
Just after 11am, a power fault disrupted train service between Outram Park and Farrer Park stations on the North East Line (NEL) for about 40 minutes.
SMRT spokesman Patrick Nathan said NSL services towards Jurong East were affected as engineering staff worked to move the stalled locomotive, which prevented northbound trains from passing through the eight-station stretch.
He said a passenger train was activated to haul the faulty locomotive to Bishan Depot, and that SMRT is investigating why it stalled. He also apologised to those affected.
SMRT first sent a tweet at 6.09am to inform commuters about the disruption, which lasted for about an hour. Train service resumed along the affected stretch at around 6.53am.
Yesterday's disruption came just two days after Transport Minister Khaw Boon Wan wrote in a blog post that the NSL had gone 100 days without any major delays. He had said the milestone was especially inspiring as the NSL is the oldest of Singapore's five MRT lines.
Both SMRT and SBS Transit, which runs the NEL, deployed shuttle bus services and made regular bus services passing between the affected stations free for commuters caught in the delays.
SBS Transit spokesman Tammy Tan apologised to affected commuters, and said the cause of the power fault is being investigated.
Both operators declined to provide the number of commuters affected by the delays, both of which occurred during off-peak periods.
Medical student Sean Wu, 25, boarded a train at Outram Park to head home, and waited in it for about 15 minutes.
"It is annoying. I understand it happens, but there should be a clearer message on the estimated duration of the disruption," he said.
Mr Wu added that he was unaware of the shuttle bus services because he did not hear any announcements made at the station.
"There should have been a public service announcement at the station, not on Twitter," he said.
Mr Wu then left the train and took a bus from Outram Park to Plaza Singapura at Dhoby Ghaut for lunch, before taking the NEL home to Farrer Park.
Other commuters affected by the breakdowns took to social media to vent their frustrations.
Facebook user Loh Wai Poon wrote: "Well, LTA has granted SMRT (a) later opening time on Sundays for six months to give it more time to do maintenance and improve its system. Hope it gets some good result at the end of the six months."
Another user, Gopi Gopal Pathi, said: "Pity those people who travel to work and school. Some are going back home from night shift."
•Additional reporting by Rachel Oh