A jeweller in London said on Wednesday there's a good chance that diamonds worth millions of pounds were snatched by thieves from a vault in the city over the weekend, British broadcaster Sky News reported.

Police said on Tuesday that heavy cutting equipment had been used to break into a vault containing deposit boxes at Hatton Garden Safe Deposit Ltd., home to London's diamond trade and to other types of gem specialists.

According to the Sun newspaper, it's believed the burglars tunnelled their way in through one wall to access a lift shaft at the building on Friday at the start of the Easter weekend.

Rappelling shaft to underground

They then rappelled down to the vault in the basement, according to the paper. They would have had four days to crack open a 45-centimetre-thick metal door and rifle through the boxes.

Police gave no details of what was stolen, but the Sun said the haul could be as much as 200 million pounds ($300 million US, or $370 million Cdn), dwarfing the amounts taken in Britain's previous biggest heists.

"Robbery at one of the biggest safe deposits in Hatton Garden over the Easter weekend," London gemologist Thelma West wrote on Twitter. "The loss is huge."

Gerald Landon, a London-based jeweler who kept jewelry, gems and cash in a box at the site, told CBC's Carol Off that he's had trouble getting information and at the moment, doesn't even know if his was one of the boxes opened.

"I'm hoping I'm one of the lucky ones that hasn't been broken into," he said.

He said he's baffled as to how it happened and said he feels the thieves must have had inside help who knew the layout or a potential weak spot in the system.

"With the amount of surveillance cameras in Hatton Garden, you would think something would be shown," he said in an interview on As It Happens.

Not all insured

"Everybody's shocked and there's going to be some big tears because there's a lot of money people have lost and they're not insured," jeweller Michael Miller told Sky News.

Miller told the Guardian newspaper that some depositors use Hatton Garden and skip insurance to reduce costs and that his property stored there was uninsured. He said he feared the crime has cost him up to 50,000 pounds ($92,000 Cdn) in lost jewellery, including a collection of watches.

"The last time this happened here was 2003," he said, referring to a heist at the same location when a criminal posing as a customer emptied a number of deposit boxes and made off with 1.5 million pounds ($2.7 million Cdn) in valuables.

Police said the latest burglary was reported on Tuesday morning when jewellers opened for business.

Former Flying Squad (commercial armed robbery division of the Metropolitan police) chief Barry Phillips told Sky News that police will be looking for forensic and material evidence at the scene of the theft.

The jewellery district has been hit by other noted burglaries in the past. In 1987, two armed robbers made off with an estimated 60 million pounds ($111 million Cdn) worth of jewels.