The gang behind a smash and grab raid on an exclusive jewellery store stole valuables with an estimated retail value of £380,000, police said tonight.
The thieves snatched the haul from the De Beers store in the Royal Exchange shopping arcade in the City of London.
One source said the gang also grabbed some watches from a branch of Omega almost as an after-thought in the five-minute raid.
It is understood the shopping courtyard was protected only by wrought iron gates joined by a chain and padlock more suitable for securing bicycles.
Once inside, the gang used sledgehammers to smash down two sets of glass doors before battering their way inside the De Beers store adjacent to the exit.
The shopping arcade, based around a champagne and seafood bar, is lined by jewellers and luxury goods stores which often leave displays fully stocked to encourage window shopping.
The thieves struck at 10pm on Saturday when a red BMW pulled up outside the Grade I-listed Royal Exchange, just yards from the Bank of England.
Police believe they used boltcutters to remove the chain and padlock securing the iron gates at one of the four entrances before attacking the glass doors.
Investigators are examining CCTV images from the arcade and surrounding streets, as well as number plate recognition cameras, in a bid to identify the car.
Police officers worked through the night at the store to gather forensic evidence and catalogue what was stolen and how much it was worth.
City of London Police, which is responsible for policing the square mile, said tonight no arrests had been made.
Detective Chief Inspector Steven Chandler said: "We are currently following a number of lines of inquiry and I can reassure the public that every effort is and will be directed to bringing those responsible to justice.
"We need the assistance of the public in tracing the car used in the offence, the criminals involved and the items stolen."
The Royal Exchange, built in 1565, is located between Threadneedle Street and Cornhill and boasts more than 30 luxury stores, including Gucci, Hermes and Cartier.
It also includes a branch of Tiffany & Co, a common target in smash and grab raids, where an alarm is also believed to have been triggered. Nothing was taken.
The robbery was the latest in a spate of similar raids at jewellers in the capital, many including masked gangs wielding sledgehammers and riding mopeds.
In a separate incident, De Beers and Tiffany & Co stores were raided in the Westfield shopping complex earlier this year, with thieves making off with an estimated £2 million of gems.
The Mozafarian store in Knightsbridge, west London, was targeted last August, when raiders stole more than £1 million of jewellery.
Earlier this month the gang behind Britain's biggest jewellery theft was jailed.
Four men were convicted of stealing 43 pieces of jewellery worth £40 million from Graff in London's Mayfair.