The young man was attacked on the Vejlby Centervej road in the Risskov area of the city, just outside Aarhus Handelsgymnasium upper secondary school.
His injuries are not life-threatening, East Jutland Police have confirmed.
Shortly after the incident, police arrested four men on board a city bus. They are suspected of violent assault. The incident is related to an internal conflict, police wrote on Twitter.
Det er formentligt en intern strid, der var årsag til knivstikkeriet. Fire mænd blev anholdt i en bybus efterfølgende, og de er p.t. sigtet for grov vold. #politidkhttps://t.co/H9le7RxOOz https://t.co/2aqvJ2zMsK
— Østjyllands Politi (@OjylPoliti) August 26, 2019
The victim had recently started his first year at the school, fellow students told TV2 News.
Upper secondary schools (Danish: gymnasier) are typically attended by young people between the ages of 17-19, between state school and university.
According to witnesses, the 17-year-old was approached by four or five masked men who were carrying pepper spray and knives. He was stabbed in or near his back and went to the school’s canteen to find help, TV2 Østjylland reports.
Aarhus Handelsgymnasium wrote on social media that students and staff had been briefed and that counselling would be offered to those who felt they needed it.
“The students who witnessed the attack have today, Monday, been offered psychological support, and on Tuesday a psychologist will… give a group debriefing,” the school wrote via its Facebook page.
“Students who need personal consultations will be offered this,” the message also said.