The North-South MRT line ended 2018 with a glitch that affected service during the morning peak yesterday, and persisted with delays well into the evening.

As early as 7.43am, commuters started posting on social media sites such as MRT Disruption Feed, Tata SMRT and Twitter about a track fault between Bishan and Ang Mo Kio stations.

"You don't deserve the six more cents," wrote one commuter, referring to the latest fare adjustment that kicked in last Saturday.

Another wrote: "Left home earlier but... wasted effort."

Similar posts continued past noon, when another commuter posted to say train speed was still slow, adding that a train had remained at Ang Mo Kio station "for five minutes now".

Others said they had seen SMRT maintenance staff at the station.

Checks by The Straits Times found that southbound trains were still packed at 10.30am, a sign that the line may still be recovering from the early-morning glitch.

When ST checked again at 2pm, the situation had not improved.

Northbound trains were terminating at Yishun station, a sign that SMRT was sending more trains southward to clear the build-up.

At Ang Mo Kio station, trains remained at the platform for several minutes before moving off.

Once in motion, they crawled at around 5kmh to 10kmh towards Bishan, picking up speed only halfway through the journey.

At 4.30pm, commuters were still complaining of delays. At Ang Mo Kio and Bishan stations, commuters were informed of a "track fault" over the public announcement system. Asked about this, SMRT would not elaborate.

Eight hours after the incident surfaced, spokesman Margaret Teo said in a statement: "There are speed restrictions imposed for commuter safety from Ang Mo Kio to Bishan MRT stations (southbound only) due to track maintenance work earlier this morning."

At 6.07pm, SMRT said on Twitter that "due to track maintenance work, southbound trains from Yio Chu Kang to Bishan are travelling slower till end of service". It asked commuters to add 10 minutes of travel time to their journey.