Train services from Jurong East towards Kranji station were restored at about 9am on Monday morning, operator SMRT said on its official Twitter account.
Free buses, which were activated to cope with the overcrowding that occurred on train platforms between Admiralty and Ang Mo Kio stations, remain available. SMRT also sent empty trains to the affected stations to ease the overcrowding.
Train services were delayed on Monday morning's rush hour on the North-South Line towards Marina Bay station due to a track circuit failure.
SMRT said on its Facebook page that the track fault caused trains to travel at slower speeds between Kranji and Yew Tee stations. Its engineers were deployed and the faulty track circuit was fixed at 8.32 am.
Meanwhile, commuters took to Twitter to voice their displeasure over the delay. Many said they took much longer than their usual travelling time to get to their destinations, with one user commenting that he took over two hours to get from Bukit Batok station to Toa Payoh station.
The squeeze was so severe at Yishun station that the upriding escalators had to be shut down for safety reasons.
Republic Polytechnic also made arrangements for its students who were scheduled to sit for a test at 8.30am on Monday, but were late due to the train delay, to take the test on another day.