The assault ocurred at Church Street, near Main Street, in Portlaoise at around 12.30pm yesterday afternoon.
A man in his 70s was arrested at the scene and is being held at Portlaoise Garda station.
The scene is currently being preserved for a technical examination.
Gardaí are appealing for for witnesses or anyone with dash cam footage to come forward.
Leading the investigation is a Senior Investigating Office and an incident room has been established at Portlaoise Garda Station.
The incident occured just metres from Independent TD Brian Stanley's constituency office.
Stanley told RTE that it is not the "type of thing that normally happens here. People are shocked by it. I think people are very sad about what's happened."
