At least 20 students were injured Wednesday at a high school in the State of Pennsylvania in the United States.

The police have detained a suspect, apparently a student at Franklin Regional High School, in a suburb of Pittsburgh. The suspect stabbed some of his classmates.

The victims, some of them with serious injuries, are between 14 and 21 years old and have been moved to hospitals in the area.

The school was closed by the police.

“A critical incident has occurred at the high school. All elementary schools are canceled, the middle school and high school students are secure.” reads a statement drafted by officials from the school after the incident.

Four students are serious, while others suffered scratches and cuts during the chaos that followed the attack, said Dan Stevens, emergency management spokesman.

The  television images from the scene showed students standing in groups outside the school, a mile from ambulances.

One parent said that his daughter called him “frantic” to tell him that one of her friends had been stabbed at school in Murrysville.

“One never expected this to happen,” he said, adding that he believed that the community was safe.

The suspect, a male student, has been taken into custody for questioning.