It happened in Crossgates, Leeds at 12.50pm today (Wednesday) and the two male suspects fled the scene in a grey vehicle with some money. Police confirmed that no-one was injured.
They were described as white males, between 5ft 7” and 5ft 11” and were wearing grey hoodies and jogging bottoms.
Det Insp Phil Jackson of Leeds CID, said: “This was a terrifying incidents for the people inside the building society, thankfully no-one was injured.
“We are appealing to anyone who may have been in the vicinity and may have witnessed this incident to come forward and speak to the police to assist with our enquiries.”
Witnesses should contact Leeds CID via 101 quoting log number 0685 or Crimestoppers on 0800 555 111.