Thieves may have got away with a record haul of diamonds after a brazen heist in London's diamond district netted an estimated £200 million worth (275 million euro, $300 million) of gems, media reported Wednesday.

Burglars broke into a vault at a safe deposit centre in Hatton Garden, where many jewellers had left their stocks over the long Easter weekend, and cracked open 70 secure boxes, the police said.

Earlier reports put the number of boxes raided at 300.

A security guard heard an alarm go off on Friday, a bank holiday when the shops would have been closed, but shut it off when he failed to spot any sign of a disturbance, media reported Wednesday.

The Sun newspaper quoted a Hatton Garden insider saying: "It is estimated that around £200 million in diamonds, jewels and cash were stolen."

Hatton Garden is the centre of London's jewellery industry and has been home to hundreds of shops and manufacturers since the 19th century. The De Beers diamond company also has offices there.

One jeweller, Michael Miller, feared he may have lost up to £50,000 of uninsured jewellery and watches in the raid, only discovered Tuesday after the holiday break which coincided with Passover, when many of the area's Jewish diamond cutters and dealers were also away.

"There is a double-door entry and a locked system to go in. You have to go through two doors to get in the place and then get into the vault," he told reporters.

He added: "I have a collection of watches I was going to give my son and that is irreplaceable."

Another, Norman Bean, added that he was "shaken" and "devastated".

Reports suggested that the thieves may have hidden inside the building, emerging after staff went home to abseil down a lift shaft and smash into the vault.

Members of the London police's Flying Squad -- the unit which deals with heists and armed robberies -- are investigating.

Roy Ramm, a former Flying Squad commander, told the BBC that the raid had a "certain old-fashioned audacity about it".

Ramm said he "would not be surprised" if the value of the heist was as high as £200 million.

But he added that the true value may never be fully revealed and suggested that, as well as legitimate items of jewellery, items kept in such vaults could include firearms and drugs.afp