A man armed with a sledgehammer robbed a building society in Berkshire after smashing his way inside.
Two couriers were loading a cash machine at Nationwide in Station Hill, Maidenhead, early on Tuesday.
The raider forced his way inside and threatened the guards with the sledgehammer before fleeing with an undisclosed amount of money.
The man is believed to be white and was dressed all in black, including a black balaclava and black gloves.
Det Con Jonathan Groenen said: "Thankfully neither of the couriers were harmed during this incident, though they were obviously left shaken by what happened.
"This attack would have caused a significant amount of noise as the robber forced his way into the vestibule.
"I would like to speak to anyone who was in the area at the time who may have seen or heard anything in connection to this incident."