A gang of four thieves wearing balaclavas smashed their way into luxury jeweller De Beers, in the Royal Exchange, with sledge hammers in a five-minute raid on Saturday night.
They targeted diamonds before breaking into neighbouring watchmaker Omega in a move described by one source as an afterthought.
The dramatic CCTV images released by the police show the men piling handfuls of jewelery into white sacks and scouring the stores for the most expensive items.
The thieves then made their escape in the same red BMW they arrived in.
Police sources, including a former member of the Scotland Yard Flying Squad, are speculating the gang may have had an inside man who tipped them off about security weaknesses.
Royal Exchange, which houses some of London’s most expensive retailers, was allegedly protected by only a small lock and a series of glass doors.
Police are now sifting through hours of CCTV footage in a bid to track the men.
A City of London police spokesman said: “The force is treating this incident very seriously. A team of dedicated detectives from the City of London Police is currently involved in the investigation and is liaising with other police forces.”
The spokesman added: “One of the reasons this type of crime is rare in the City is the protection offered by the network of CCTV cameras that cover the City. These include private cameras in and around the Royal Exchange, which officers are now analysing as one line of enquiry.”
Police are appealing for witnesses or information leading to the capture of the men or their vehicle. No arrests had been made last night.