The latest incident — which left the driver and 15 passengers shocked but unhurt — occurred as the bus travelled west along Charleston Drive at around 7.50pm last night.

Police said today they were hunting three youths — all thought to be between 15 and 17 — who were seen running off down Arran Drive following the incident.

The incident is the second snowball attack on a bus reported to the police in the past week.

Last Saturday, a snowball was thrown through the open window of another bus being driven along Commercial Street. The driver was struck in the face and had to carry out an emergency stop.

Two suspects — both male and thought to be in their mid to late teens — ran off along Commercial Street and into Gellatly Street.

The driver went to Ninewells Hospital having suffered scratches to his cornea. He is expected to make a full recovery.

Anyone who has information regarding either incident is asked to call Tayside Police on 0300 1112222, or speak to any officer.