A man has attacked a six people, including a police officer, with a knife at a market square in the south-west 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.