A suspect injured four people with a knife at the Hamm-Lippstadt University of Applied Sciences in the western German city of Hamm on Friday.

The alleged perpetrator was apprehended by students in a lecture hall, who then held him until the police arrived. The suspect is a 34-year-old man, said a police spokesman.

What do we know about the attack?

Three women and one man were wounded in the attack.

According to authorities, one victim's injuries were so serious that they were flown to a hospital by helicopter.

It is still unclear whether an attacker is or was a student at the university. The possible motive for  the attack is also not yet clear.

According to initial reports, the suspect entered a university building around 3:30 p.m. and attacked people in the corridors. Then he went into a large lecture hall where he was apprehended.

The emergency services warned on Twitter: "We are on site with strong police forces and ask you to avoid this area."

The university opened the cafeteria for shocked students, offering free drinks and chaplains. The aim was "to provide the best possible support for the students," university chancellor Sandra Schlösser told a local newspaper, Westfälischer Anzeiger.

The Hamm-Lippstadt University of Applied Sciences has existed since 2009. It has 5,600 students across two campuses in Hamm and Lippstadt, both in west Germany. The campus in Hamm is located in the east of the city.

The incident comes just days after a deadly car ramming in Berlin, where a 29-year-old driver struck a crowd of people in the German capital. A school teacher was killed and around 30 others were injured — including 14 students who were on a school trip.

dh/rs (AFP, dpa)