Transport operator SMRT issued a statement on the rail crack that delayed services on the North-south line on Monday evening - some 20 hours after the incident. SMRT said northbound service between Marina Bay and Orchard stations was delayed on April 29 because of the crack.

"Our findings revealed that a rail joint on a stretch of track between Somerset and Orchard stations had cracked, resulting in a track circuit break, which in turn activated a safety mechanism in the signalling system," the statement read. Its engineers "temporarily installed G-clamps to secure the rail joint" where the crack was.

Trains travelled over the affected stretch at a slower speed as a safety precaution so as not to put pressure on the G-clamps, added the statement. At 11.02pm, trains along the affected stretch were able to travel up to 40kmh until the end of train operating hours, it said.

SMRT has since replaced the affected rail, and trains have been operating at their normal speed of 80kmh from Tuesday morning. SMRT added that the reason for the rail crack is still being investigated.