Singapore's troubled metro system was hit by fresh disruption on Saturday, two days after a severe breakdown that required emergency evacuations of people trapped in trains.

Metro operator SMRT Corp gave no reason for the latest disruption, which affected services in the Orchard Road shopping belt and Raffles Place financial district.

A passenger named only as Jeannie was quoted as saying on local broadcaster Channel NewsAsia's website that she and other commuters were asked to leave their train and walk along the underground tunnel to the nearest station.

An estimated 127,000 commuters were affected when a power fault hit the same North-South line on Thursday, in what is believed to be the worst breakdown in the metro's 24 years of operation.

Then, stranded passengers had to endure a one-hour wait inside stalled trains before being freed and the entire outage lasted about five hours, although no-one was injured.

SMRT, which also runs taxis and buses, further enraged the public when an electronic message went out to its cabbies during the outage saying there was an "income opportunity" to ferry stranded train passengers.

Saturday's breakdown took place after Transport Minister Lui Tuck Yew expressed disappointment at SMRT Corp's handling of Thursday's incident.

"This is a very, very serious disruption and better take heed, learn the lessons, improve on the systems," Lui said in remarks published Saturday in the Straits Times.

The publicly listed metro operator is 54 percent owned by state investment agency Temasek Holdings, as of March 2011.

Singapore has a population of just over five million. Most are dependent on public transport because of the prohibitive cost of cars.