Twenty-one people have been charged for trespassing, drug possession, and carrying graffiti cans and house breaking implements since the central metropolitan district crime team commenced an operation investigating damage caused to a number of historical buildings.

Eighteen people are due to appear in the Perth Magistrates Court, fourteen move-on notices have been issued and three people have received juvenile cautions since the police probe began.

The Swanbourne Hospital in Mount Claremont is the latest venue which has been damaged and police believe the repair bill from the vandalism will cost millions of dollars.

Police will continue to target the anti-social behaviour of this nature and told WAtoday.com.au that buildings around Perth are being sought out as a place to "hang out and cause damage" rather than host parties.