Two buses serving the number 39 route through Leigh Park, in Havant, had several of their windows broken by rocks as they were driven along Park House Farm Way at 4.30pm on Saturday.
No passengers were onboard either service and the route was diverted via Middle Park Way for the rest of the day.
A spokesman from Hampshire Constabulary said the force is appealing for information from the public.
He said: ‘We can confirm that officers were called out to an incident at 5.32pm yesterday evening following reports of criminal damage caused to a number of Stagecoach South buses on Park House Farm Way.
‘A number of items have been thrown at the bus as they drove down Park House Farm Way just after 4.30pm.
‘Were you in the area at the time? Did you see what happened?’
Anyone with information is asked to call 101, quoting reference number 44210018025.