Witnesses described scenes of panic and confusion when the man -- who authorities said was a 31-year-old Swiss-Turkish national with a history of psychological problems -- suddenly began stabbing people at the main train station in Winterthur, Switzerland's sixth largest city, during the morning rush hour."I am exceptionally calling this a terrorist attack," Mario Fehr, in charge of security in the Swiss canton of Zurich, told a press conference.Regional police commander Marius Weyermann agreed, telling reporters it was "clear from the scene that the motive for this act must be sought in the realm of radicalisation and extremism".He said police had received the first emergency call at 8:28 am (0628 GMT) and that the suspected perpetrator was arrested by 8:33 am.The man, identified as Nesip Dedeler, had been checked into a psychiatric clinic earlier this week before he showed up at the Winterthur station, wielding a knife, authorities said.He injured three men, aged 28, 43 and 52, with the eldest seriously wounded by stab wounds to his thigh and forced to undergo emergency surgery, Weyermann said.Swiss President Guy Parmelin said he was "shocked by the terrorist attack... This deeply affects me". "I wish the three injured a swift and full recovery. And I thank the emergency services for their work."'Goosebumps'Images broadcast by several Swiss media outlets and on social media showed a man with long dark hair and a full beard running in front of the station shouting "Allahu akbar!" (God is the greatest), while raising his right hand.A 65-year-old taxi driver named Turhan Muslu told the Blick newspaper that he witnessed the attack.