The three, aged 15, 17 and 18, were held at an address in Camden, north London, on suspicion of conspiracy to commit burglary.
Smash-and-grab raiders targeted branches of De Beers and Tiffany & Co at the Westfield centre in Shepherd’s Bush, west London, in the early hours of Wednesday.
A masked gang of up to 10 people used sledgehammers to bash their way into the complex through a fire door.
They then ran to the two ground-floor stores, both in The Village, where Westfield’s premium stores are located, before smashing open windows and doors.
Police and security guards were alerted by automatic alarms as the gang sped off in at least three stolen cars, one of which was later recovered in north-west London.
One police patrol was involved in a high-speed chase with a vehicle but lost sight of it in residential streets around the mall.
Witnesses said window displays and glass cases were cleared of valuable jewellery, understood to include necklaces, rings and bracelets, many of which were studded with diamonds.
A Metropolitan Police spokeswoman said the three suspects were being questioned at a west London police station.
Detectives have been studying CCTV from a large number of cameras at the complex and in surrounding streets to try to identify the culprits.