“Brazen” ram-raiders smashed a van into the front of Tiffany & Co in London before they fled on mopeds with “significant” amounts of jewellery.
The Ford Transit was driven into the shop in Sloane Square, Knightsbridge, at about 03:00 BST, before being abandoned, the Met Police said.
No arrests have been made and police are appealing for witnesses.
An employee at Tiffany & Co said the firm was assisting police but could not comment further.
Workers have put barriers around the broken window at the shop on Sloane Street.
Det Insp David Watkinson, said: “This was a brazen and targeted incident which has resulted in a significant amount of items stolen.
“Although the incident took place overnight, it is a busy well-lit area.”