"The safety of students at the school can not be guaranteed. The students behave in classrooms but outside during recess and in the recreational room it is a very disruptive situation and there are a lot of conflicts," Catharina Niwhede, the district's director of the teachers' union in Malmö, told Swedish Radio News.
The ball is now in the court of the administration, because the school closing can only be ended by the Swedish Work Environment Authority.
The approximately 200 affected middle school students have been informed of the situation. But it is still unclear what will happen with them.
According to the union, the situation began to become untenable after another school, Örtagårdsskolan, was closed last autumn, which led to many students from that school being placed in Värner Rydenskolan.
The acting education chief for Malmö city, Hans Nilsson, told news agency TT that representatives on the school board had already attempted to work out the situation with the principal and staff to see what solution could be found. But the situation was so critical that the school was closed down.
"Certain groups of students were so disruptive that the teachers could not handle it," Nilsson said.
Malmö city is now going to hire a security company to make the school safer. Staff will even receive help with security routines and conflict resolution.
Nilsson also said that some students may be expelled from the school, or moved to different schools.