A police spokesperson said: “Due to the damage at the site, the evidence was inconclusive and the cause remains undetermined.
“As part of our enquiries, we are keen for anyone who saw the fire in its early stages – especially prior to emergency services arriving on scene – or anyone with drone footage and photographs, to contact us.”
At the time of the blaze, a number of nearby properties were evacuated and residents were warned to close windows and doors to prevent smoke from entering their properties.
The fire service initially described it as a “large-scale incident”.