The company behind plans to turn Strathmartine Hospital into luxury flats say people are “hell-bent” on breaking into the site.
Robert Evans of building company Muir Smith Evans said chisels, masonry drills and even sledge hammers have been used to get into the building.
There was a fire in the building on Wednesday night. Although police say it was not suspicious, Mr Evans said security teams employed by his firm regularly encounter people trying to get into the site.
He said: “The listed building is continually being secured and checked by security on a regular basis.
“But people who want to enter have gone to great lengths to gain access.
“Breeze blocks have been installed to stop people entering, but they have been kicked in.
“Things like sledge hammers, chisels and even a masonry drill have been found on the site, which people have used to get into the listed building.”
The Scottish Government approved plans to build hundreds of homes on the site of the former psychiatric hospital in September last year.
The plans had originally been approved by Angus Council despite strong opposition from neighbouring Dundee City Council.
Dundee City Council claimed the plans for 222 homes were in potential conflict with its own 20-year housing strategy.
In a rare move, Angus Council’s decision was then called up for further scrutiny and determination by Scottish Government ministers.
However, they granted approval in September.