The bus, service No. 155 which had its engine switched off, was parked in the berth at about 11.20pm when the bus captain got out of his cabin to help a commuter and her child find a missing bag.

However, according to SBS Transit, the bus captain failed to properly engage the handbrakes and the bus rolled out of the berth and towards Toa Payoh Lorong 4.

It rolled some 60m before coming to a stop after its rear wheels mounted the pavement in front of Toa Payoh Gardens.

The sight of the unmanned reversing bus bewildered motorists who honked to warn others of the oncoming vehicle.

One motorist, Ms Neoh Chong Eng, said in an e-mail to The Straits Times:'I heard a loud continuous honking from the vehicle next to mine. I had to stop to let this strange reversing SBS 'cross the road'.'

She said that it was only after the bus had come to a complete stop that she spotted a child, followed by a man and a woman running to the front of the bus.

SBS Transit's director of corporate communicatons Ms Tammy Tan said: 'The bus captain may have been doing a good deed at that point but he should have been more careful with the brakes.'

She added that disciplinary action will be taken against him.

No one was injured in the incident and no damage was done to the surrounding property or the bus.