Up to 20 cars were damaged when part of an Audi showroom collapsed.
A section of the first floor, covering the workshop area of the showroom on Northfield Drive, Milton Keynes, gave way at about 12:00 BST.
No-one was injured. The fire service attended to assess what happened.
The Jardine Motors Group said everyone was evacuated from the building and the company was "investigating the cause of the collapse and the extent of the damage".
Ian Wilson, from Buckinghamshire Fire and Rescue, said staff had a "lucky escape" thanks to the actions of their colleagues.
"People working within a workshop heard a loud bang and promptly hit the fire alarm call point, which was quick thinking on their part," he said.
"Within 20 minutes a third of the floor above the workshop collapsed."
Mr Wilson said there was a ramp up to the first floor, which was "serving as a car park".
Structural engineers are assessing the damage.