Up to five men escaped with the money from the NatWest depot in Tamworth.
The thieves wore masks or crash helmets and high visibility jackets as they drove a skip lorry into the building, smashing through a wall late on Wednesday night.
No weapons were used and no one was hurt.
"The raid was over very quickly. Thankfully no one was injured," Detective Inspector Bob Titley said in a statement.
The area has been sealed off for forensic examination and detectives are appealing for help in finding a car and motorcycle used as getaway vehicles.

Copyright Reuters, 2006