Police were alerted just before 3pm and all traffic has been stopped in the area.
The man was walking across Norrbro in front of the royal palace and began to lash out at people with an axe and a catapult. He attacked a car with his axe.
“Nobody has been hurt but the man has a rope around his neck and he’s tied the other end to the bridge. He’s threatening to jump,” said police spokesman Björn Engström to TT.
Police have several negotiators at the scene and they are currently trying to talk the man into giving himself up.