Train commuters grappled with delays and crowded platforms on the North-South Line (NSL) during yesterday's morning rush hour due to a train fault.

Complaints surfaced as early as 7.30am, with commuters reporting on social media about a train fault at Bishan station.

Photographs of jam-packed platforms at several stations, including Admiralty, Ang Mo Kio, Woodlands and Yishun, were tweeted.

There were announcements made on trains at City Hall station about a train fault, but no official announcement was made on SMRT's Twitter or Facebook pages about the fault.

Manager Neal Ang, 38, told The Straits Times he was at Yishun station at about 8.40am when he saw that the platforms were overcrowded.

"Some gantries were closed and the escalators were stopped to manage the crowd," he said.

The last reported train fault on the NSL was on Monday morning, when a defective train ran past the platforms at Bishan and Ang Mo Kio stations.

This led to delays for commuters.

Transport Minister Khaw Boon Wan, as he delivered a ministerial statement in Parliament on Tuesday to address recent lapses in SMRT's maintenance regime, said train operating hours on the North-South and East-West lines (NSEWL) will likely be shortened, including on weekdays, to give rail engineers more time to replace and upgrade their ageing assets.

He said this will "squeeze out more engineering hours" and help the Land Transport Authority and SMRT "speed up" projects to renew core components on the 30-year-old NSEWL.

"Until all these key ageing systems are replaced or renewed, the NSEWL remains at risk of major disruptions, even with diligent maintenance," Mr Khaw warned.

SMRT did not respond to The Straits Times' request for comment by press time.