Police failed to provide further information regarding the robbers or their motives.
The theft marks the second occasion in which this particular bank branch was robbed.
On September 12, 2011, three gunmen held up the bank during the early morning hours.
UBS is the biggest bank in Switzerland, operating in more than 50 countries.
The Swiss bank is infamously known for paying USD 1.5 billion in fines after some of its employees tried to rig the LIBOR rate – short for London Interbank Offered Rate – in several currencies, which affected borrowers around the world.