Robbers dug a 30-metre tunnel into the vault of a Berlin bank, German police have said.
The criminals escaped with the contents of safety deposit boxes, setting fire to the tunnel as they left to destroy any evidence.
Berlin police spokesman Thomas Neuendorf said the tunnel led from an underground garage into Volksbank's safe deposit room.
Mr Neuendorf said the tunnel was "very professional" and must have taken weeks or possibly months to complete.
It was elaborately constructed and even had ceiling supports.
Police were alerted to the break-in early on Monday when a security guard noticed smoke coming from the deposit room.
Mr Neuendorf said officers were still trying to determine what valuables had been stolen from the deposit boxes.