An eight-year-old has reportedly been critically injured and three others hurt seriously in a knife attack that has sparked a massive police manhunt.

The eight-year-old child, who was apparently the most seriously injured in the attack in Germany, suffered "15 to 20 cuts and stab wounds all over the body and head." The possibility of life-threatening injuries still cannot be ruled out, wa.de reports.

Police have reportedly released pictures of a man, 20, they want to speak with in connection with the attack, in which the mum of the children was also hurt.

A spokesperson for the Dortmund public prosecutor's office told wa.de it strongly advises against approaching the man directly. They said: "Anyone who sees him should immediately call the police on 110. It cannot be ruled out that he is armed."

The attack was allegedly committed in an apartment on Zentrumstraße in Bergkamen-Weddinghofen. According to police, the 26-year-old female resident and her four children, aged 3 to 8, were seriously injured by stab wounds and slashes. "The suspect, whose name is known to the police, fled the scene in an unknown direction," the statement reads.

He is described as 1.85 meters tall, slim, wearing dark clothing, with a white hat, glasses and a "three-day beard".