STOCKHOLM (AP) — Swedish police said Monday at least two people were injured and one person has been arrested in Malmö, Sweden’s third largest city, after an incident at a high school.

Police said the situation was under control, adding they had responded to ” a suspected serious crime.” The Aftonbladet daily said students were being kept inside classrooms.

Swedish broadcaster SVT said it was unclear what had happened but several people reported were injured. The students had gathered at the school to work on a musical after 5 p.m., SVT said.

“This is absolutely terrible,” school principal Fredrik Hemmensjö told the daily.