The police were alerted just after midnight that about 20 people were involved in a large brawl on the school grounds.
There was stabbing to the left and right, so four people are in hospital with stab wounds, of which two are seriously injured, says Michael Lindh, duty officer at the police.
The case is being investigated as attempted murder.
When the police arrived at the scene, only a few people were left and only one of the stabbed. The other three injured had taken themselves to the hospital.
The police arrested eight people after the big brawl. Of the eight, four had needed hospital care.
On Sunday afternoon, seven of the arrested had been detained. The eighth person arrested has not yet been interviewed. The man is seriously injured and is sedated. His injuries are not life-threatening, according to the police.
All those involved are men in their 20s-25, except for one boy who is 15 years old.
