Firefighters worked through the night to battle a huge blaze at a former north-east hospital.
The fire service were first alerted to the blaze, at the derelict Glen O’Dee hospital, Banchory, at 11.30pm last night.
No one was injured but significant damage has been caused.
Today the police have confirmed they are treating the incident as suspicious and appealing for witnesses.
Detective Sergeant George Nixon said: “While the value of the damage has not yet been established this was a significant fire which has caused extensive destruction to a listed building.
“We are treating the fire as wilful and would appeal to anyone who saw anything unusual or suspicious in the area yesterday evening or has any information to contact police on 101 as soon as possible.
“This type of behaviour will absolutely not be tolerated. It goes without saying there is a significant risk of harm with such irresponsible behaviour.”
A number of crews, consisting of 65 firefighters, and 10 appliances, were initially sent out to currently at the scene.
They worked through the night and a Scottish Fire and Rescue Service spokeswoman said five appliances remained at the scene this morning.
“They are dampening down the site”, she added.
A NHS Grampian spokeswoman said: “Firefighters have scaled back their attendance extinguishing the fire at the derelict, unoccupied building on the Glen O’ Dee Hospital site, Banchory.
“Thanks to the great efforts from our staff, all patients in the main hospital remain safe and comfortable away from the fire.”