The Dulnain Bridge establishment includes a garden centre, gift shop, cafe and antique shop. The alarm was raised around 8am on Friday. Some 40 firefighters attended. No-one was injured in the incident.
An investigation into the cause of the fire is underway.
Station manager Robbie MacDougall said: "Our crews have completely surrounded the fire but the operation is likely to continue into this evening.
"Flames spread rapidly through the building and the fire was already very well developed when first responders arrived.
"Our teams have been working extremely hard to protect adjacent maintenance buildings from the intense flames and we will continue the firefighting operation until it's brought to a safe conclusion."