She had stepped off the bus to retrieve her daughter's artwork which had fallen on the ground while they were queueing at the interchange.
But before Madam Sabrina Ng could re-board the bus, its doors closed and the bus moved off with her frightened three-year-old daughter still on board.
"I was shocked. I couldn't run after the bus so I went to the control station and explained the situation," said the 30-year-old who works in human resources.
Madam Ng was reunited with her daughter after 40 minutes of panic and hysteria.
Madam Ng and her daughter, Sara, had boarded SBS bus service 241 at Boon Lay Interchange at about 7pm on Feb 4 to take them home to Jurong West Street 92, which is about 10 stops away.
The bus was not crowded and they sat near the front of the bus.
But just as the bus driver started the engine, Sara told her mother that her artwork that she had done in class had fallen on the ground where they had been queueing.
Madam Ng told Sara to wait in the bus while she went to retrieve it.
"I asked the bus driver if he could open the doors as my daughter had dropped something just outside. I saw that he was Chinese so I spoke to him in Mandarin," she said.
Madam Ng claimed that from the driver's facial expression, "he was not happy" and "looked reluctant" to open the door, but he eventually did so.
Madam Ng stepped out to retrieve Sara's belongings, but before she could board the bus again, it started to move off.
Panicking, Madam Ng went to the control station, where they managed to track down the bus and confirm that her daughter was on board.