Chilling footage from the scene in south-west Germany showed a knife-wielding man waving the weapon around while shooting over to another man who stood nearby.
News website Schwaebische reported the man is believed to have marched into the picturesque square before stabbing people picked at random.
A person is being treated for life-threatening injuries.
Victims were discovered by police to have been laying 50 metres apart.
Police are on the scene and have cordoned off the area.
One man has been arrested in the town’s Marienplatz square.
A clip of the man brandishing a knife was posted on Twitter along with images of the bloodied scene.
The identity of the alleged attacker is yet to be released by police.
German police have refused to comment on the incident until they gather all the evidence and information from witnesses.
This is a breaking news story.
More to follow…