A driverless shuttle bus hit an aircraft tow tractor inside a restricted zone at Hong Kong airport on Tuesday, marking the second collision involving the unmanned vehicles in two months.

The accident, which did not result in any injuries, occurred around 3pm when the bus, which was not carrying any passengers, detected an obstruction and came to a stop.

According to the Airport Authority, a duty officer mistakenly instructed the bus to resume its movements, resulting in a minor collision with the rear of a stationary tow tractor that had partially extended into the driving lane on the apron.

Photos posted online by an individual showed the scene of the collision.

A preliminary investigation found that the tow tractor was parked at a designated stand but its rear end protruded into the driving path.

The bus’s sensors identified the obstruction and halted to avoid crossing into the opposite lane.

Following protocol, the vehicle issued an alert to the Integrated Airport Centre and manual intervention was required.