At least 20 students were injured Wednesday morning in a stabbing incident at Franklin Regional Senior High School near Pittsburgh.

Four people were flown to hospitals by helicopter, according to CNN.

A message on the Franklin Regional School District’s website states that all of its elementary schools were closed after the incident, and “the middle school and high school students are secure.”

Authorities say they have a suspect in custody.

Information on what led to the stabbings and the conditions of the injured have not yet been released. The students range in age from 14 to 17.

The school is in Murrysville, about 15 miles east of downtown Pittsburgh.

Students from the school are being released to their parents.