Update 2.26pm: A forensic technical examination of the scene at Vernon Mount will be carried out today, according to a Garda statement.
"A number of people were reported to have been in the area at the time and Gardaí will like these people to come forward to assist with the investigation," the statement added.
"Anyone with information should contact Togher Garda Station on 021 4947120 or the Garda Confidential line 1800 666 111."
Update 11.36am: Engineers inspecting the wreckage of Vernon Mount House have declared the area unsafe for forensic inspections.
It is unclear at this stage when any inspections by gardaí and other State bodies can begin at the historic building, which was gutted by fire last night.
Gardaí investigating a fire at historic Vernon Mount House in Cork are treating it as suspicious.
However, they are awaiting the results of a forensic examination before deciding on the direction of their inquiry.
The house, which was built in 1784 and has panoramic views over the lower Lee Valley and estuary, was engulfed by flames last night.
Emergency services got the call to the blaze in what is now a derelict building shortly before 10pm. Eight fire brigade units tackled the blaze for almost 10 hours before bringing it under control early today.
Garda technical experts will begin an examination of the property once it has been deemed safe by a safety expert.
One line of inquiry is that it may have been caused by the lighting of a bonfire on the grounds of the site.
According to Cork Past and Present (an online service of Cork City Libraries), the condition of the house has deteriorated since the mid-20th century, mainly due to wood rot, roof damage, rain ingress, and vandalism. It has been unoccupied for some time.
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Occasional efforts have been undertaken by Cork County Council to arrest the decline.
Vernon Mount House has appeared in the World Monuments Fund list of 100 most endangered sites.
The current owner was refused planning permission to build houses on the site in 1997 and it has been lying idle since.