Mortlake police Sergeant Matthew Laxton said the damage was caused overnight Tuesday to the old church at the corner of Shaw and Church streets and reported to police by a passerby on Wednesday morning.

He said the old church was sold off about two years ago and was being used as a home.

"Entry was gained through a double glazed glass sliding door which was smashed and jemmied open," he said.

"It appears the intent was to cause damage. Nothing was stolen  and an unknown implement was used to smash holes in plaster walls and to damage an internal door."

Sergeant Laxton said the total damage bill would be about $4000.

"The offender has ignored alcohol and other items of value in the old church and left after causing the damage," he said.

"The church was unoccupied at the time. C​rime scene police officers attended and inquiries are ongoing.

"We are pursuing a number of lines of investigation."

Sergeant Laxton requested that anyone with information contact the Mortlake police station or Crime Stoppers on 1800 333 000.