Scotland Yard has begun an investigation after safety deposit boxes in a central London vault were raided over the Easter weekend.
A statement from the Metropolitan Police said heavy cutting equipment had been used to get into a vault at the premises in Hatton Garden.
Officers from the Flying Squad are currently at Hatton Garden Safe Deposit as the investigation continues.
Up to 300 safety deposit boxes at the premises are thought to have been broken into. The suspects are believed to have used a lift shaft to gain access to the vault.
Sky’s Crime Correspondent Martin Brunt said: “I’m told that there are 600 boxes on the premises, 300 of which have been raided.
“The suspects have had perhaps several days (over Easter weekend) in which to get in. One report I’m told suggested that they used a lift shaft at some stage to get into the centre, which must be pretty heavily protected.
“It’s probably going to be some days before we get an idea of exactly how much has been stolen or what indeed has been stolen.”
The area is known as London’s jewellery quarter.