The incident took place near Konkuk University Station at 6:20 p.m. when the streets were still crowded and chaotic from the evening rush hour.
The mother alerted the bus driver of the situation but was only let off at the next stop.
The incident was shared on the bus network’s online bulletin board by another passenger on the bus who had witnessed the mother weeping in distress wanting to leave the bus to find her daughter.
After criticism exploded over social media, Seoul Metropolitan Government called the driver of the bus and inspected CCTV footage from the vehicle.
The bus had kept the exit door open for 16 seconds before shutting it and taking off on a 10-meter drive to an inner lane and then a 20 seconds further drive to the next stop.
“Based on the video recordings, it appears that the bus driver only became aware of the situation after the bus changed lane. He seems to have decided it was safer to let the woman out at the next designated stop,” said a city official in a statement to the media.
The official added that the inspection had only just begun, and that more details of the incident would be examined over time to determine the safety issues that had been at stake.