The Straits Times understands that the power went out after lunchtime, and a train with passengers on board was stuck in the tunnel. It was moved to Bishan MRT and passengers were evacuated within four minutes.

Service on both sides of the line was down for about 10 minutes before it resumed.

Trains started rolling through the line's first five stations - Marymount, Bishan, Lorong Chuan, Serangoon and Bartley - on Thursday morning, with the first train arriving at 6 am.

The remaining 24 stations will open from next year.

About 55,000 commuters are expected to use the line's first five stations. Daily ridership will climb to about 500,000 when the entire line is running.