Four people were injured in a knife attack on a university campus in Germany on Friday, police said, adding that the perpetrator has been detained.

Police are conducting a "major operation" in the area of the Hamm-Lippstadt University of Applied Sciences where "several people were injured with a knife", they wrote on Twitter, asking people to avoid the area. 

A police spokesman told AFP four people had been injured but could not say how badly.

According to the WDR broadcaster, the perpetrator was a young man from Hamm who attacked several students with a knife inside a seminar building. 

Three women and one man were injured, WDR said, before other students managed to restrain the attacker.

A bloodstain was visible on the ground outside one campus building, the Westfaelische Anzeiger reported.

In a separate incident on Friday, a woman and a seven-year-old girl were seriously injured in a knife attack at an elementary school in Esslingen, near Stuttgart.

Germany was also shocked earlier this year by a rare shooting on a university campus.

An 18-year-old student opened fire in a lecture hall at Heidelberg University in southwestern Germany, killing a young woman and injuring three others before fleeing the scene and turning the weapon on himself.