The guards were delivering money to Swedbank on Hamngatan in the heart of the capital’s shopping district.
“There were two suspected assailants, who made their getaway on a moped,” said police spokesman Kjell Lindgren.
Police say they do not know whether the raid occurred inside the bank or on the street. The two masked men threw a secure cash bag on the ground as they left the scene.
“We have opened an investigation into a serious robbery at 11:25, and have brought technicians and police to the scene. The victims and witnesses are being questioned,” said police spokeswoman Ann-Charlotte Wejnäs.
It is not yet known whether the robbers were armed or whether they made away with any valuables.