A man has attacked a number of people with a knife at a market square in the southwest German city of Mannheim, police say. One of the people injured was anti-Islam activist, Michael Stürzenberger, who had been preparing to hold a rally in the square, according to his group. The incident was caught on a YouTube livestream and showed the attacker stabbing a man, and then a police officer who went to help. The officer is in a critical condition. The attacker was shot and injured by another police officer. German Chancellor Olaf Scholz described the incident as “terrible”, and that his thoughts were with the victims. He posted on X: “Violence is absolutely unacceptable in our democracy. The perpetrator must be severely punished.” Police in Mannheim tweeted about a "major police operation" in the city"s market square and a rescue helicopter was sent to the scene. One person attacked several others with a knife, injuring them, at 11:35 (10:35 BST), police said in a follow-up statement. A firearm was then used against the attacker, it added. The attack is understood to have happened at the same time as a rally in the market square hosted by far-right anti-Islam activist, Michael Stürzenberger, and his organization the Citizens" Movement Pax Europa (BPE). A spokeswoman for the city of Mannheim confirmed that the organization had registered an event on the market square for Friday morning. BPE confirmed to Bild newspaper that Stürzenberger was attacked in the leg and face. His colleague Stefanie Kizina told the newspaper that Stürzenberger had to undergo surgery, but his life was not in danger. "The attack happened before the event even started, it must have been planned well in advance," she said. Police have not released any further information about those injured in the attack. According to DPA, a police officer was in critical condition and will have to undergo emergency surgery. A livestreamed video from the event shows a man attacking people with a knife. At least one person is seen with a wound to the leg. A number of bystanders are seen grappling with the attacker, who later manages to break free and stab a police officer in the back. Several police officers with firearms then surround him, before he falls to the ground. According to Bild, Michael Stürzenberger is the author of an Islamophobic blog, as well as a member of the BPE, an organization which says it stands against the "Islamization" of Germany. The 58-year-old is one of the authors of the anti-Muslim platform PI-News and is being monitored by the Bavarian domestic intelligence service. A former politician, Stürzenberger once led a small right-wing populist party Die Freiheit, which was dissolved in 2016. Before that, he was a member of the Christian Social Union (CSU) -- the Bavarian sister party of the Christian Democratic Union (CDU) -- but left before he was kicked out. — BBC