Northbound train services between Marina Bay and Toa Payoh stations resumed at 11.30am on Wednesday morning.
The Land Transport Authority in a statement said that a "small localised fire" in the tunnel involving electrical wiring disrupted train services on the North-South line at about 9.05am. The fire was about 5m away from the northbound platform of Newton station.
Some smoke from the fire escaped into Newton station, but there was no fire in the station itself, said LTA.
The Singapore Civil Defence Force (SCDF) put out the small localised fire at 10.06 am, and no one was injured. Bus bridging and free regular bus services are currently available between the affected stations for commuters who are affected.