MURRYSVILLE, Pa. -- At least 20 people -- 19 students and one adult -- were injured Wednesday morning in a stabbing incident at Franklin Regional Senior High School in the Pittsburgh area, said Dan Stevens, an emergency management agency spokesman.
The stabbings happened in classrooms and a hallway, he said, adding that a suspect -- a male who is a 16-year-old sophomore at the school -- was in custody.
WTAE-TV in Pittsburgh reported at least four medical helicopters transported victims from the school. Five local hospitals are treating victims.
Shortly after the stabbing was reported, students started posting grim photos like the one below on Twitter.
Of those injured, seven male teens and one adult male were being treated at Forbes Regional Hospital, Dr. Chris Kaufman said. He said the injuries were "quite serious" and that "some are clearly life threatening." The teens had stab wounds to their torsos, abdomen, chest and back areas, he said.
Kaufman said two of the victims being treated at Forbes Regional were sent to surgery almost immediately on arrival. Those two patients had low blood pressure, he said. A third was being prepared for surgery and the rest were being evaluated to see whether surgery was necessary, he said.
Forbes Regional Hospital later said several students have deep penetrating injuries. Forbes Regional Hospital chief medical officer Dr. Mark Rubino said he expects all seven stabbed teenagers who were taken there to survive, "but I do want to stress the critical nature of their injuries."
Ambulances could bee seen swarming the school for most of the morning, ferrying those injured students to nearby hospitals, as seen in the photo below.
Forbes CEO Reese Jackson told WTAE that one female student saved another student's life by applying pressure until medical personnel could arrive.
University of Pittsburgh Medical Center said it has 11 patients from the stabbings at four of its hospitals. UPMC did not release information on the ages, genders or conditions of the patients it is treating.
Stevens said all of the injures are stabbing-related, such as lacerations or punctures. There were no guns involved in the incident.
Information on what led to the stabbings was not immediately released. Stevens said detectives interviewed the suspect as to a motive in the stabbings. WTAE later showed the suspect being transported in a police vehicle.
The suspect was handcuffed by a school resource officer, Murrysville Police Chief Thomas Seefeld said. WTAE reported that Vice Principal Sam King tackled the suspect, leading to his apprehension.
Seefeld said the suspect used two knives in the attacks and was being treated for injuries to his hands. Police say they arrived to the scene with multiple victims in a first-floor hallway, including a male security guard who had a stomach wound but was not stabbed.
A student at the school told WTAE that students heard alarms for a fire drill, then screams from the stabbings. BuzzFeed later reported that student Nate Scimio, who reportedly took the photo below at a nearby Chidlren's Hospital and posted it to Instagram, was instrumental in pulling the alarm that alerted others to the stabbing.
The school is in Murrysville, about 15 miles east of downtown Pittsburgh. The school was releasing students to their parents after the incident, Stevens said.
WTAE says the incident happened about 5:20 a.m. MDT in the science wing of the school.
Bill Rehkopf, a KDKA radio host and Franklin Regional High School graduate, reported on air that he was shocked by the stabbings.
He kept thinking, "It doesn't happen here, it can't happen here," he said. The tweet below came from Rehkopf
He said he was seeing parents showing up at the school and an increasing media presence. Parents appeared to be calm, he said. Another KDKA reporter said she spoke with a parent who said she received a cellphone call from her daughter, who told her mother that "something bad" happened and that she needed to be picked up.
There were several photos taken from inside the auditorium of a nearby elementary school, where students from the evacuated high school were waiting to be picked up.
CNN contributed to this story.