The perpetrators threw the rocks so hard they littered the floor on the other side of the hall. About 40 to 50 rocks were used to smash the large southern side windows, which each have three panels.

Chair of the Showground Trust, Ian Armstrong said the windows were smashed between 4pm and 4.30pm on Monday.

He got a call from a woman who lives near the showground advising him that someone was breaking the windows. He came straight into town.

“This is what I found,” he said.

“It’s a real mess. It makes you cranky.”

He said there have been minor problems at the showground in the past, but nothing as significant as this latest incident.

Mr Armstrong has been involved with Oberon Showground since 1947 when he worked on levelling the arena.

He has been volunteer with the showground trust for a very long time.

Heritage Hall is used by the whole community. All kinds of functions, from 21sts to wedding receptions, are held there. The next event to be held at the showground will be a campdraft on December 13.

Oberon police are currently investigating the incident.