Southbound MRT services between Woodlands and Ang Mo Kio were delayed from 6.25am Thursday morning by a rail crack - the third in recent weeks.
SMRT spokesman said the crack was detected between Yio Chu Kang and Ang Mo Kio stations, and that G-clamps have been used - as previously - to temporarily stabilised the affected area.
Travel time was delayed by as much as 40 minutes between Woodlands and Ang Mo Kio, but has now been reduced to 15 minutes. Nevertheless, the slower trains are expected to affect crowding on all southbound stations down the line during the morning peak.
SMRT said it is investigating the incident.
Rail cracks have been rare in the Singapore network till recently. Before the last three incidents, there was an average of only one crack per year.