A signalling fault occurred between Lorong Chuan and Caldecott on the Circle Line, causing delays for commuters during the morning peak hour on 21 May 2021.

Notifying commuters about the delay on Facebook at 6.36am, SMRT wrote: "Our engineers were immediately deployed and are working to rectify the fault. Trains are moving at a much slower speed."

On Twitter at around 7:30am, SMRT wrote: "Train services have resumed. Free regular and bridging bus services have ceased. We are sorry for affecting your morning commute." In all, delays lasted for about one hour.

During the affected period, SMRT made announcements in-train and at affected stations, advising commuters to add additional travelling time between Serangoon and Farrer Road. Commuters were also encouraged to make alternative travel arrangements, including taking other train lines.

SMRT said that free regular and bridging bus services were available between Paya Lebar and Buona Vista MRT stations.