Operator SBS Transit said in a press statement that a power fault in overhead wires between the underground Outram Park and Harbourfront stations caused the breakdown.
The affected stretch covers a third of the Sg$4.6 billion ($3.75 billion), 16-station North East Line that opened in 2003.
It typically see thousands of commuters during the morning, lunch and evening rush hours.
SBS said train services were stopped at 10.14am (0214 GMT) to enable repair work. Services are expected to resume at 4:30pm before the evening peak hours.
“We currently have about 30 engineers on the ground working on repairs,” SBS stated.
Singapore’s metro service has been roundly lambasted after a series of breakdowns since December 2011, including three disruptions in as many days in April.
An 11-hour disruption along the North East Line in March 2012 left 90,000 commuters stranded.
Thursday’s disruption coincided with an announcement by the Land Transportation Authority (LTA) that it intends to raise the maximum penalty for each train incident currently pegged at Sg$1.0 million.
A high-level inquiry that followed the December 2011 breakdowns found out that Singapore’s metro system has been plagued by outdated equipment and poor maintenance for years.