Sergeant Kevin Davidson, of Mosgiel, said a trailer carrying a cabin became detatched from the ute towing it in Factory Rd about 10.30am.
The runaway trailer veered to the left, away from oncoming traffic, hit the veranda of Headway Design and came to rest in vacant car parks.
''It was fortuitous there was no cars in those parks,'' Sgt Davidson said.
The crash was a result of a pin connecting two parts on the trailer coming out.
No-one was injured in the crash and the sagging veranda would be braced pending a safety inspection.
Police were investigating the cause of the crash.
Salon owner Kathleen MacDonald said the sound of metal being dragging along the road caught her attention and she saw the cabin head towards the salon and crash into the veranda.
That the cabin and trailer missed any vehicle or pedestrian was ''sheer luck'', she said.
''It was a fluke.''
