A 16-year-old student at the school in the Enskede neighbourhood has been arrested over the incident.
“We are in crisis management right now,” Ingela Wihlner, who is on the school board, told TT.
“There are quite a lot of people who saw parts of the chain of events,” said Sven-Erik Olsson, a press spokesperson for Stockholm police.
The 17-year-old victim arrived in Sweden as an unaccompanied refugee minor, and his legal guardian and the people who took care for him at his accommodation have both been informed of his death, police said.
The stabbing took place at lunchtime on Wednesday. The school board decided to close the school for the rest of the day but said it would be open again as usual on Thursday, the local education authority told TT. Police officers will be in place at the school throughout Thursday, after having cordoned off the area where the attack took place.
Police do not yet know what provoked the argument, and were working on a technical investigation on Wednesday afternoon.
“We were contacted about a fight at the school. Before we could get there, we were informed that one person had been stabbed, and that turned out to be correct,” said Sven-Erik Olsson.
The victim was driven to Karolinska hospital in the capital, but passed away there, and police are investigating the incident as a murder.
The 16-year-old suspect was arrested close to the school shortly after the incident.
No more information about the suspect has been released, but police spoke to several students who saw the fight. On Thursday, students will be given information and will have the opportunity to talk about what happened.
“I feel really terrible,” one teacher at the school told TT.
Anna Ekström, Sweden's Minister for Upper Secondary School and Adult Education and Training, told the newswire: “I receive this awful news with sadness and dismay. My thoughts go to the victim and those close to him. Then of course I think of all the students and teachers at Enskede gård high school.”
She also said that the government was not currently planning to take any acute measures, but would be following the incident closely.
Prime Minister Stefan Löfven also commented on the boy's murder. “It's dreadful, a tragedy. I'm thinking of the boy who lost his life and of his relatives. For the school, staff, and other students, it must be a dreadful incident,” he said.