The Land Transport Authority (LTA) and public transport operator SBS Transit are investigating the over six-hour-long disruption to train services on the North East Line (NEL) that affected peak-hour traffic yesterday morning.

Initial investigations show the delay was due to a broken contact wire that affected power supply to trains launching from the Sengkang depot, said SBS Transit in a statement.

Train services at three MRT stations were affected - Punggol, Sengkang and Buangkok - and SBS Transit said it operated a shuttle train service on one platform between these stations from 5.36am, the start of train service.

To supplement the shuttle train service, the operator also provided free bridging bus services at designated bus stops at the affected stations.

Repair works were carried out after the morning peak period and the operator said it shut off power supply to the train tracks between Hougang and Punggol MRT stations to facilitate repair works. It announced the temporary closure of the stations at 10.40am.

In the meantime, shuttle trains ran between Serangoon and Hougang MRT stations.

Repair works were completed by 11.49am and normal service resumed at 12.14pm, said the operator. It added that there was regular train service between HarbourFront and Serangoon MRT stations, which ran at a frequency of about nine minutes during the train service disruption.

The operator apologised to affected commuters for the inconvenience caused.

The measures were, however, insufficient to completely ease the crowd build-up during the morning peak hour at Punggol and Sengkang MRT stations, which are the main hubs of two LRT networks.

Some commuters reported delays of up to 40 minutes in their journeys. Mr Chew Zhi Kang, 30, was one of the commuters who was turned away at Buangkok MRT station after SBS Transit stopped all train services there for repair works.

"The (service staff) said (the service) was only down from Punggol to Buangkok, so I thought it would be safe to take (the train) at Buangkok," said the engineer.

"I missed the bridging bus and never expected it (the breakdown) to last so long."

Some commuters said the directions given by SBS Transit staff were confusing. The signboards at the stations did not display the train's end destinations, and commuters had to rely on the service staff's announcements to figure out where each train was headed.

Undergraduate Angie Peh, 20, said she was directed by SBS Transit staff to take the free bridging bus service to Buangkok MRT station to hop on the NEL, but by the time she arrived, the station had been closed for repair work.

"They have a lot of staff helping to redirect people so that's good, but for the older generation, some were very confused," she said.

With hordes of commuters redirected to the free bus services, some expressed concern over possible exposure to the coronavirus.

Madam Hor Mei, 68, was in a snaking line of commuters waiting for the bridging bus service at Sengkang MRT station.

"Usually there are not so many people here," said the retiree. "I've got my mask, but I was a little afraid of the crowd."