Criminals took advantage of the quiet Christmas period to drill into the vault of a retail bank in Germany, stealing at least 10 million euros ($11 million) in cash and valuables from customers’ safe deposit boxes, police said Tuesday.

The perpetrators drilled through a thick concrete wall ‌at a branch of Sparkasse bank in ‍the western city of Gelsenkirchen and then broke into several thousand safe deposit boxes and stole a sum estimated in the double-digit millions of euros, the police said in a statement.

Most shops and banks close in Germany over the Christmas period, starting from the evening of Dec. 24, and police only discovered the hole after a fire alarm went off in the early hours ⁠of Monday, Dec. 29.

Dozens of angry customers gathered in front of the bank on Tuesday loudly chanting, "Let us in!"

"I couldn't sleep last night. We're getting no information," one man told the Welt broadcaster as he waited outside the branch, adding that he had been using the safe for 25 years ‌and that it contained his savings for old age.

Another man said he used his deposit box to store cash and jewellery for ​his family.

A spokesperson for the Sparkasse bank in Gelsenkirchen ‍did not immediately respond to a request for comment.

Police said witnesses have reported that they ‍saw ​several men on ‍Saturday night carrying large bags in ⁠the stairwell of an adjacent parking ‍garage.

There were also reports of a black Audi RS 6 leaving the garage early on Monday morning with masked men inside. The vehicle's licence plate was that of a ⁠car stolen ‌in Hanover, more than 200 kilometres to the northeast of Gelsenkirchen, police said.