Police say a 16-year-old boy "was flashing two knives around" when he injured 19 students and a school police officer who eventually subdued him with the help of an assistant principal at a high school near Pittsburgh.
Investigators haven't determined a motive but say they're looking into reports of a threatening phone call between the suspect and another student the night before.
Dr. Chris Kaufman says two victims were in the operating room and one was awaiting surgery at Forbes Regional Medical Center, a few miles from Franklin Regional High School in Murrysville.
Officials say four students were believed to be the most seriously injured Wednesday
|Students walk down the street away from the campus of the Franklin Regional School District, where several people were stabbed at Franklin Regional High School, on Wednesday, April 9, 2014, in Murrysville, Pa., near Pittsburgh. . (AP Photo/Gene Puskar)
A woman walks onto the campus of the Franklin Regional School District . (AP Photo/Gene Puskar)
Students leave the campus (AP/Gene Puskar)
Jenna Mickel, right, a sophomore at Franklin Regional High School, right, stands with her father, Richard, as she talks with reporters near the school, where several people were stabbed. (AP Photo/Gene Puskar)
A policeman directs a driver to the area to pick up students on the campus of the Franklin Regional School District where several people were stabbed at Franklin Regional High School on Wednesday, April 9, 2014, in Murrysville, Pa., near Pittsburgh. The suspect, a male student, was taken into custody and being questioned. (AP Photo/Keith Srakocic)
Stevens said not all of the 20 injured were cut by the knife, though most were. Some suffered scrapes and cuts in the mayhem that ensued at Franklin Regional High School on Wednesday morning. Stevens says it doesn't appear any students suffered life-threatening injuries.
While Stevens said all the injured are between 14 and 17 years old, hospital officials told CBS Pittsburgh the patients they were taking in from the incident range from 15 to 60 years old.
The suspect, a male student, was taken into custody and being questioned. Stevens says the suspect used a knife, though he didn't say what kind or why he attacked the others.
The incident occurred around 7:13 a.m.
Three air medical helicopters hwere dispatched to the scene as well as dozens of ambulances.
According to a witness, the stabbings happened in the science wing of the building.
Franklin Regional school district has canceled all elementary classes and say that high school and middle school students are secured.
The suspect was being questioned by county detectives and police at the Murrysville police station. Stevens said the suspect used a knife, though he didn't say what kind and said it wasn't immediately clear why the student attacked the others.
One student told WTAE he saw "students holding their stomachs, bleeding." That student wasn't sure how the assailant was stopped, but said at some point, a fire alarm was activated and said, "As soon as we heard the fire alarm was pulled we went outside."
Speaking outside the school, Morris Hundley said his 14-year-old daughter, Morriah, called him Wednesday morning in tears. Hundley came to the school still wearing his slippers, hoping for more information.
"My first thoughts were I think we need to home school now that this has happened," Hundley said. "The words can't describe how I feel. I'm just thinking of the victims."
Gov. Tom Corbett instructed state police to assist local investigators.
"I was shocked and saddened upon learning of the events that occurred this morning as students arrived at Franklin Regional High School. As a parent and grandparent, I can think of nothing more distressing than senseless violence against children. My heart and prayers go out to all the victims and their families," Corbett said in a statement.
School officials and Murrysville police didn't immediately return calls seeking further details, but the school issued a bulletin on its website saying: "A critical incident has occurred at the high school. All elementary schools are canceled, the middle school and high school students are secure."
The district later announced that the high school students were being moved to another school in the district, where their parents could pick them up.
The district serves about 3,600 students who live in the bedroom communities of Murrysville, Export and Delmont. The elementary and middle schools are part of the same campus.
Stevens said the incident happened after most students had arrived but before the school day was officially in session.
Initial reports indicated the stabbings happened during a fire drill, but investigators now believe another student may have pulled a fire alarm to alert others to the emergency in hopes that would clear the building.
Parents and former students say the school, which doesn't have metal detectors but does spot searches when security officials deem it necessary, generally does a good job of keeping students safe.
"I think the school reacted as fast ... as possible," said Rich Nickel, whose daughter, Jenna, 16, is a sophomore. "It's obviously a (lone) individual's act."