Passengers in one of the MRT trains on the North-South Line on Monday evening were shocked when a door was left open while the train was travelling between stations.
Videos on social media showed that a door on one side of a carriage was fully open as the train was moving from Ang Mo Kio station towards Yio Chu Kang station.
SMRT confirmed that the incident happened on Monday at around 7.30pm.
The station manager was inside the train and at the door handling a train door fault when he made an error that allowed the train to move off from Ang Mo Kio station with its door open, said SMRT.
After the error was made, the station manager immediately kept all commuters away from the door, and in-train announcements were made to tell commuters to keep clear of the door area and to hold on to grip poles, said Ms Margaret Teo, vice-president of SMRT corporate communications.
Ms Teo added that the train stopped shortly, after travelling around 200m, and returned to Ang Mo Kio station, where all commuters disembarked safely.
Safety is SMRT's top priority and the station manager was suspended with immediate effect, said Ms Teo.
"The train was immediately withdrawn from service," she added. "We are sorry that this incident happened."
In 2016, an LRT train door opened while the train was travelling from Bukit Panjang to Senja amid a five-hour service disruption.
SMRT said then that the cause could have been a design flaw.
The incident happened after a signalling fault during commuting hours forced SMRT staff to override the driverless Bukit Panjang LRT system and drive the trains manually.