A loud boom that startled residents along the Sengkang LRT system last night was caused by a power outage, The Straits Times understands.

No one is believed to have been hurt in the incident, although some commuters had to get out of a train and walk along the tracks.

One passenger on the train, who gave her name only as Mrs Lim, told ST that the train was quite empty, with fewer than 10 people.

She was with her husband and two children on the train, which was travelling from Kangkar LRT station towards Bakau LRT station. About halfway through the journey, it started bumping violently, she said.

"There were a lot of sparks. The air-conditioning went off and some of the lights as well," said the 40-year-old, who works in the education sector.

They tried contacting SBS Transit staff through the intercom, but communications were breaking up on the system, she recounted.

Her husband and another man in the train opened the emergency door and the commuters got out.

Eyewitness Haziq Rahmat Ali, a 20-year-old student, said that he was in his room at 8.10pm when there was "a huge flash of light", followed by a loud boom.

"I thought it was lightning," said Mr Haziq, who lives at Block 123B, Rivervale Drive, adding that the Singapore Civil Defence Force and the police arrived soon afterwards.

Ms Tammy Tan, senior vice-president of corporate communications at SBS Transit, told ST that train services on the Sengkang LRT system were down at 8.04pm due to a power fault. Power was switched off on the Sengkang East loop for checks.

"We are investigating the cause of the fault. We apologise to affected commuters for the inconvenience caused," she said.

Free bus rides and bridging bus services were available during the disruption.