Cops were only alerted early on Monday morning, when a fire alarm was triggered inside the branch of Sparkasse bank in Gelsenkirchen.
By then, the culprits were long gone.
Investigators believe the burglary likely took place during the Christmas holidays or even the previous weekend.
When emergency services eventually did arrive, they discovered a massive hole drilled through the vault wall.
Investigators say the masked gang – believed to consist of two or three – entered the building via a parking garage.
From there, they cunningly made their way through several secured doors before reaching an archive room adjacent to the vault.
Using professional-grade equipment, the gang drilled through an 18 inch reinforced concrete wall to access the treasure inside.
Experts estimate the operation would have taken somewhere between two and four hours.
The criminals are thought to have used a 20kg industrial drill fitted with a synthetic diamond-coated crown.
“You can’t buy that kind of drill at a hardware store,” a police spokesperson said.
They would also have needed jerry cans, hoses and a pump to cool the machinery during the drilling process.
Once inside the vault, the thieves emptied as many safe deposit boxes as they could before escaping through the hole they had created.
At the time of the break-in, the vault reportedly housed around 3,300 safe deposit boxes of varying sizes, rented by approximately 2,700 customers – some of whom held multiple boxes.
Police believe up to 90 per cent of the boxes were breached.
Each box is insured for up to €10,300, meaning the bank could theoretically face losses of as much as €33,990,000 (£30,000,000) million.
The bank said the focus is now on contacting affected customers and processing the fallout from the burglary.
“Reaching out to customers is our top priority,” the spokesperson said.
“We will definitely be contacting all safe deposit box holders.”
Authorities are appealing to the public for any information.
“The extent of the damage is currently under investigation,” a spokesperson for Gelsenkirchen Police said.
“This includes securing forensic evidence and looking for possible witnesses who may have heard suspicious noises or observed anything unusual in recent days.”
As part of extensive enquiries, police are analysing vehicle movements and interviewing local residents.
Unfortunately, the investigators say there are promising leads at this time.
This case has drawn comparisons to the infamous Hatton Garden heist in London in 2015.
A group of elderly career criminals drilled through a 20 inch vault wall to steal millions in cash, jewellery and valuables.
In doing so, they bypassed some of the world’s most sophisticated security systems.
Although most of the gang was jailed, a significant portion of the loot was never recovered.
