Emergency crews were called to the blaze in Kilmarnock’s King Street on Monday night.
No one was injured, but a number of businesses have been impacted by the destruction.
The four-storey building partially collapsed, with East Ayrshire Council confirming parts of the listed property would need to be demolished “as a matter of urgency” to allow for recovery works and further assessments.
Police are treating the fire as wilful and have arrested and charged a 12-year-old boy in connection with the incident.
A force spokesperson said: “The youth has been released on an undertaking to appear at Kilmarnock Sheriff Court later this month.
“The fire is being treated as wilful and enquiries are ongoing.”
Emergency services were alerted to the fire shortly before 9pm on Monday.
At the height of the blaze, the Scottish Fire and Rescue Service (SFRS) mobilised six appliances and specialist resources.
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Douglas Reid, leader of East Ayrshire Council, thanked the efforts of the emergency services as he announced a recovery fund would be implemented to support businesses affected.
On Thursday, the local authority said “recovery work continues apace with demolition taking priority over the coming days”.
The demolition will be carried out in two phases.
In the update, the council reported: “Police Scotland have confirmed this is no longer a crime scene.”
